Son Goku in Dragon Ball is was originally a Saiyan named Kakarot, and was sent to Earth as a baby to clear it of all life. He was adopted by Grandpa Gohan, and after hitting his head, became a powerful hero and the champion of Earth, with no memory of his past.
Mazinger Z: Erika. She was an android built by Dr. Hell. However, she suffered from amnesia and had forgotten her origins. She genuinely believed she was a normal girl, and when she was told her true nature, she rejected it. In the end she helped The Hero Kouji and she died because of it.
Zero from Tenchi Muyo!. She ended up fusing with the person she was emulating.
The motivation of Captain Kuro in One Piece, who wanted to give up the life of piracy to become a normal (albeit rich) man. Not so much a Face-Heel Turn considering how he wanted to do it, though... turns into a cruel subversion when he seems to consciously invoke this trope in a confrontation with the girl he intends to kill to make her drop her weapon
Sogeking, in the same series. This is a literal case of becoming the mask for Usopp, who undergoes a heavy personality shift when he dons the Sogeking mask. This leads to a funny exchange where the Usopp and Sogeking parts of his personality have an argument while he's trying to think of a plan.
This series actually has a running theme of declaring oneself to be something and then using that as a source of strength to follow through. Sogeking, Luffy, Don Krieg, etcetera
Note that she still tried to deny, right up to the breaking point. The Straw Hats were already in the middle of The Government's stronghold (Luffy himself had personally wrecked over 1000 rank and file soldiers, Roaring Rampage of Revenge style. But then, he's Luffy. He's either in Idiot Hero mode or Roaring Rampage of Insert Emotion Here). So Robin STILL tries to talk them out of it. Luffy insists that they're going to rescue her anyway, and then she can leave the Straw Hat Pirates if she wants. And then... Tear Jerker ensues. Robin's tears, specifically, in a moment of Not So Stoic. Also, Pirate on Elite Assassin Team action.
Nami as well. She had only intended to use Luffy for all he was worth before leaving. But the longer she stayed with them, she grew to like being part of the Straw Hats (especially compared to her experiences with Arlong). Eventually, she betrayed them and cheerfully took off with Going Merry. But when on her own, she broke down and cried.
Mami in Sister Princess is a spy charged with disrupting the reunion of Wataru and his sisters, pretending to be another sister; at the climax of the series, she is the one who takes the action necessary to keep the family together, rejecting her own real brother — the mastermind of the scheme — to beg Wataru to come back home.
Played with in Irresponsible Captain Tylor. Tylor finds out Harumi is a Raalgon spy early on, but makes the decision to keep it between them and trust her despite her inevitable betrayal — something that completely confuses her. It's explicitly because of this response that Harumi begins having second thoughts that leads her to an official Heel-Face Turn.
Kurama of YuYu Hakusho was a kitsune before he died and inhabited the body of an unborn human child. He planned to run away from his human "mother" Shiori Minamino when his demonic powers returned, but realized that he loved her too much to leave.
In Shugo Chara!, Mr. Nikaidou is a spy for Easter who infiltrates the school. While he has no compunctions with backstabbing the heroes whatsoever, he is eventually defeated, and following the ensuing Defeat Means Friendship he immediately goes back to the school, performing the role he was using as his guise with no-one the wiser.
Subverted, deconstructed and played with in Code Geass.
Never one to be content with mediocrity, Lelouch vi Britannia wore and became not one, but two different masks through the series' run, one being Zero and the other being LelouchLamperouge.
Between the two seasons, Lelouch is brainwashed into becoming Lelouch Lamperouge, the ordinary if highly intelligent high school student. Except that he's still disaffected with society and only superficially apathetic to the dreary, distasteful reality of Britannian domination.
Rolo, with each passing day, grows more comfortable in his role, until finally he dies for his “brother’s” sake.
In D.Gray-Man, Lavi is a successor to the Bookman lineage, who only joined the Black Order to record the war. However, as the years passed, he got more and more into the role of an exorcist, and is visibly angry when Bookman tells him he's not really a part of the Order, and that he's only there because it's convenient. His issues with Becoming the Mask are actually what Little Miss Badass Road Kamelot uses to "destroy his heart".
In Superior, the Big Bad female lead feigns hopelessness to gain the hero's trust and kill him. A few days later she realises she has a huge crush on him.
Used quite positively in Haibane Renmei. Reki originally acted nice and supporting towards everybody solely to earn a quick salvation for her troubles, but as time went by and no Day of Flight came, it slowly became her true identity, as she finally realized in the final episode, allowing her to Ascend to a Higher Plane of Existence.
Yukino Miyazawa. Her public mask which she created soon after she started school, was designed to elicit praise from those people around her. Playing the role of the perfect girl was so stressful that she had to unwind by turning into a slob at home. When Arima discovered her secret and blackmailed her, keeping her mask on became so uncomfortable that when she and Arima fell in love, she decided to throw her mask away, only to slowly discover that she acted perfect for so long that a lot of her mask persona became part of her true nature.
Arima also wore a mask of perfection but unlike Yukino, he never took his off, because he feared that his true nature was so awful that everyone would reject him if he took it off.
Happens to the fake Asuna, Shiori, in Mahou Sensei Negima!. While her Signum Bioregens supposedly makes her more-or-less a sleeper agent (which is in and of itself a subversion of this trope) with added control (she can apparently switch at will), Shiori is in danger of merging with Asuna's personality if she falls in love while disguised. Infiltrating a group held together by a Chick Magnet might not have been the best of ideas...
Also appears to have happened to Governor-General Kurt Godel, who was unambiguously heroic 20 years ago. In the meantime, he infiltrated the corrupt senate, to find out more about and stop their villainy. He has since taken on many more villainous characteristics, such as being a Smug Snake and exhibiting Fantastic Racism to an incredible degree.
Lyle Dylandy. He joins Celestial Being mostly as a Kataron Double Agent, but in the end, he becomes a full-fledged Gundam Meister like his deceased twin brother, Neil.
Also Anew Returner. She's The Mole, but falls in love with Lyle. In the end, she attempts to return to him and Celestial Being, but is controlled by Ribbons into attacking Lyle, forcing Setsuna to kill her.
Flay Alster in Gundam SEED. She pretended to love Kira because she wanted to have revenge against him for her dad's death, which he caused indirectly, but ended up loving him for real.
Katejina Loos in Victory Gundam is effectively kidnapped by the Zanscare early on. At that point, she comes up with the idea of getting close to them and becoming a spy for the League Militaire. Whether or not that would have been possible ends up being beside the point, as she slowly (or maybe a little too suddenly) becomes an actual enemy pilot and a total zealot by the end.
Zeheart Gallette of Mobile Suit Gundam AGE enrolls in a Federation high school as part of his cover (he's a Vagan spy, but is young enough to be in high school). He does this only to maintain his cover, but finds himself forming real friendships among his classmates, most especially with Asemu Asuno and Romary Stone, which continue to affect his judgement long after he rejoins the Vagan military.
In Ranma ½, Ryoga initially allowed Akane to cuddle and sleep with his cursed animal form, as a way to piss off her fiance Ranma. It backfired massively when Ryoga actually fell in love with Akane since she was so kind to his animal form, but had already doomed his chances by sleeping in her bed without her knowing it. Ouch.
Contractor Shihoko from Darker Than Black started up a relationship with Huang sometime in the past as part of a Syndicate mission. While she didn't let any feelings get in the way of the original plan, they did spark some uncharacteristic pity that lead her to pull some strings and give Huang the opportunity to join the Syndicate himself as an alternative to memory erasure.
Also the cult leader Alma in the same episode. She started out as a typically ruthless Contractor and started the Friends of the Gate as a way of hiding from Contractor-hunting humans and keeping abreast of information about the Gate. Over time, because of the faithful worshipers, she began to believe in peaceful coexistence and genuinely became the spiritual leader she pretended to be. Totally against Contractor stereotype, she was happy to bear the terrible price of using her powers (rapid aging and debilitating health) so that she could appear young before her followers, and also considered it a way to atone for her past actions.
Sena Kobayakawa of Eyeshield 21 undergoes this, taking on such a title and becoming the "Hero of Notre Dame." The more the series progresses, the more he realizes how important that name really is and how people's dreams are relying on his lightspeed runs. And of course, this leads to problems when he meets the real Eyeshield 21...s and has to fight for his title.
Ironically his ultimate opponent is not someone who is vying for the title, but someone whom already surpassed everyone whom has taken up that title.
Stewart of Sonic X was a government agent assigned to investigate Sonic and the other animals. As it turned out, while he shows himself capable as an agent, he's really good at, and really likes, being a teacher. And occasionally a Badass Teacher.
In the manhwa Aflame Inferno, creatures called Tedlars can only interact with the human world by taking over a human's body, subsequently killing the human doing so. As the Tedlars usually have to live the same life the possessed humans do to avoid detection (not to mention they have access to all the humans' memories), it's quite possible that they become the human they took over themselves. However, usually Tedlars don't stay too long in one body, avoiding this.
In episode 18 of To Aru Majutsu no Index, the guy who was hitting on Mikoto turns out to be a shapeshifting assassin assigned to kill her. He fell in love with her for real, so he decided to protect her from his colleagues, but murder Touma and get rid of his potential romantic rival. After Touma defeats him and a steel girder falls on him, he begs Touma to protect her as well.
Possible example in Shinigami from Soul Eater. He tells Asura that he took on his current silly appearance and demeanour to avoid scaring the children he wanted to recruit to his school, but that he 'got used' to it. The odd flashbacks depict him as far more ruthless and direct in his dealings with his enemies.
Sai was trained as an emotionless assassin and then sent to join Team 7. Originally ordered to assassinate Sasuke and observe Naruto, he eventually became a true member of the team.
In a darker variant, this is Kabuto's backstory. An orphan who was all but conscripted into duty as a spy, he spent most of his childhood under numerous names in different villages. By the end of it, he's not really sure who he is. When he breaks down, the village stops trusting him, he loses his only purpose in life, and ends up believing Orochimaru's insane logic.
Tobi has a decidedly literal take on this trope, in that he has become his literal mask, ie no one. After The Reveal that he is really Obito Uchiha, he just says That Man Is Dead and the heroes can call him whatever they want.
In Bakugan: Gundalian Invaders, Ren was sent by the Gundalians to get the Battle Brawlers to join them in the guise that they were the innocent party in their war. However, after experiencing their friendship and eventually realizing that the king he served didn't care about him, he did a Heel-Face Turn and joined the Brawlers in the battle against his own kind.
In Tsubasa Reservoir Chronicle, it is revealed that Fai has secretly been working as a mole for Fei Wong in an attempt to resurrect his twin brother and has been misleading the group the entire time. However, he eventually develops a genuine affection for his comrades and undergoes a Heel-Face Turn just prior to the reveal.
Played with in Special A. Megumi tries to distract Yahiro (the closest thing the early chapters have to a Big Bad) so that he won't interfere with Akira and Tadashi's burgeoning relationship. She does so by pretending to like him. Yahiro sees right through the mask, but goes along with it just to screw with her. In the process they end up actually falling for each other.
Fullmetal Alchemist has this with some of the homunculi. For instance, Pride is, as true to his name, totally bereft of compassion for any human being in the world... except for his foster mother, Mrs. Bradley, who tended dearly to him after he was hit by a car (not knowing he was a homunculus, nor about the near-immortality that comes with the territory). Doesn't mean he has any hesitation to sacrificing her along with the rest of the entire country in Father's plans, of course, but at the end of it all, he's the only homunculus left - having his Philosopher's Stone eradicated, but spared from death, by Edward Elric - and he gets grow up from scratch under her care. Wrath also shows compassion for the same woman given that she's his wife, but he doesn't have to put forth quite as much of an act as Pride does.
Yukki and Yuno in Mirai Nikki. Both of them were faking their love and using each other. Yukki used Yuno for protection and Yuno used Yukki for an emotional crutch. But over time the fake aspect became less and less fake and more like genuine love.
Ninamori of FLCL wanted for this to happen with her family. She thought if her parents would come to the play and watch it together, and they could all act like a happy family, it would become real. That was why she loved Puss In Boots so much: It represented a lie becoming a happy truth.
Souichi Negishi is a soft-hearted nice guy. His stage persona in Detroit Metal City, Krauser II, is a violent, foul-mouthed, vulgar Gene Simmons lookalike. Quite a few gags in the series revolve around Negishi accidentally lapsing into his Krauser II persona when he's out of costume, offending and confusing everyone around him.
In Ravages Of Time, Sima Yi's plan for revenge after Cao Cao has his family purged involves his assassin Liaoyuan Huo joining "a worthy lord" and using Sima Yi's money to build him up as a rival to Sima Yi's lord Cao Caonote particularly after the deaths of Lu Bu and Sun Ce, then moreso after the northern Yuan clan's downfall so that Sima Yi can work his way up Cao Cao's ranks. However, Sima Yi already admits his recognition that Liaoyuan Huo has been "want(ing) to leave this dark maze" (as Zhao Yun realized during his rescue of Zhang Lei and Sima Lang during the purge of the Sima clan residencenote "I have always wanted to crawl out of this place, crawl toward the light. For what? Living without ambition, like Zhongda; I hate that kind of life. Living from day to day, like my life; I hate that too.") and years later, in chapters 386 and 387 Huo turns on his teacher as an assassin after the teacher and his men take Liu Bei's wives and son hostage during the Battle of Changban, having by now internalized the name that Liu Bei gave him: Zhao Yun, styled Zilong.
Reiner Braun from Attack on Titan, in an absolutely heartbreaking deconstruction. His guilt over his crimes as The Mole, and growing attachment to his human comrades, results in him suffering dissociative episodes. He quite literally Mind Raped himself into having episodes where he genuinely believes his cover is real, since that's who he would rather be. Two a little more minor cases also occur with Annie Leonhart and Bertolt Hoover, his partners. During a rampage, Annie spares her former classmates... which eventually leads to her being exposed. And Bertolt eventually admits that not everything was a lie and he did care about his comrades during his Villainous Breakdown.
In the second season of Ojamajo Doremi, a young wizard by the name of Akatsuki was sent by his fellow wizards to help Oyajide kidnap Hana. To do this, he adopted a friendly facade and pretended to be Doremi's friend. But after spending a lot of time with and getting to know her, he began having doubts. When The Reveal came along and exposed his duplicity, Doremi's pain at being betrayed was one of the things that helped him and his allies, Tooru, Fujio, and Leon, make a Heel-Face Turn and save Hana from the other wizards.
Summarized in the novelization of Knightfall, Alfred explains to Tim Drake that Batman uses the cowl to become a different personality, hearkening back to primitive beliefs that wearing the mask of a god is to become that god.
(Batman puts his mask on)
Bane: Stop hiding.
Batman: I'm not hiding. I'm becoming.
By now, he's gone so far that in Batman Inc #3, El Gaucho even remarks "Why the hell is Batman masquerading as Bruce Wayne, anyway? I've met Bruce Wayne and you don't fool me."
There was also a three-part story in which Batman Became A Completely Different Mask; his undercover identity of Matches Malone. In "Close Before Striking", the real Matches Malone returns to Gotham, and gets shot by Scarface's gang, since Scarface has concluded that Malone is in cahoots with Batman. As Batman blames himself for this, he spends more time in his Matches identity, and both Bruce Wayne and Batman start adopting Matches's mannerisms and attitude. Nightwing is able to snap him out of it before he kills the Ventriloquist.
Another suggested reason why Batman keeps the Bruce Wayne persona is because it's the last little bit of humanity he has left. In Bruce Wayne: Fugitive, he tells the rest of the Bat-family that he's dumping the Bruce Wayne identity to be Batman 24/7, seeing it as a liability. Nightwing, in particular, doesn't take that well and goes at it with him. It takes encounters with both Superman and Catwoman to realize that he kinda does need Bruce Wayne.
On the other hand when the League had their personalities divided and Bruce and Batman were temporarily separated people, Batman became an empty shell, even faceless. Bruce, on the other hand, had all the rage and anger, but none of the training or ability to channel it into anything positive.
From a purely psychological point of view, this makes sense, as it's Bruce Wayne, not Batman, who suffered the trauma of seeing his parents cut down, who needed an outlet for his pain. Batman. on the other hand, didn't come into existence until Bruce had become a fully grown adult.
In the same story arc, a similar problem leads Eel O'Brian to reunite the alter-egos and reverse the process. He finds that, in the process of becoming a superhero for money (in his Post-Crisis incarnation), he grew to love the trust and respect he received. After the split, however, his old desire to commit crimes returns, making him desperate to reverse the process before he does something unforgivable.
In Generations he reveals to his son, the second Batman, that he assumed control of Ra's Al Ghul's criminal empire and changed the organization so that charities which once acted as it's fronts were now the entire operation with the criminals still working for them none the wiser.
In some incarnations, becoming the mask may be what led Dr. Harleen Quinzel to become Harley Quinn. In her origin story, Mad Love, the possibility was brought up that she interned at Arkham Asylum to cash in on the infamy of its highly abnormal inmate body. Ultimately, she really does end up giving a damn about a certain patient.
Played with with Superman. In the Silver Age, Clark Kent was the mask worn by Superman. Beginning with John Byrne's reboot, Superman became the mask Clark Kent wore.
It eventually came back around to Clark Kent and Superman both being masks that he wears. Even as Clark he has to pretend and hide things about his character and nature.
From the Marvel Universe, we have the Thunderbolts, who were originally the newest incarnation of the Masters of Evil, posing as superheroes to win the public's trust while the major superheroes were apparently dead for a year. Their leader, Baron Zemo, eventually leaked their true identities to try to avert a Heel-Face Turn before he could Take Over the World. It didn't work; the majority of the team defeated him, and tried — for various reasons — to actually become heroes. To the best of their moral abilities, anyway.
Only the first incarnation of the Thunderbolts counts as this. During Civil War the new Thunderbolts team was no longer "Reformed villains trying to actually be the heroes they'd originally pretended to be" and was instead "a bunch of violent thugs we stuck mind control chips into so we could use them for black ops" who they put under the direction ofNorman Osborn and by Dark Reign had morphed into "Norman Osborn's especially vicious group of thugs because the Dark Avengers weren't bad enough."
The Heroic Age incarnation, on the other hand, is a specific attempt by the Avengers to induce this. They're using incarcerated supervillains to do good in the hopes that they'll start liking it, and then try to redeem themselves.
Interestingly used in Lucifer, where a shapeshifter is trapped in the form of a grieving father (whom it had killed to assume his shape, to try (and apparently succeed) at killing his daughter) and gradually becomes more the grieving father than the ancient shapeshifter from before the universe. This doesn't seem come about entirely honestly, though — much of the father's mentality seems to be forced onto the shapeshifter by the same magic that traps it in his form.
Rorschach later describes the early years of his hero career as "I wasn't Rorschach then. Then I was just Kovacs. Kovacs pretending to be Rorschach". During his bail hearing he refused to respond to anything other than "Rorschach". He also refers to his mask as his face, and once referred to removing it as "removing the skin from my head". He's kinda sensitive about it.
"It was Kovacs who closed his eyes. It was Rorschach who opened them again." If that doesn't define this trope, nothing does.
It was portrayed wonderfully with the art too, when the reader sees Rorschach in the past, he stands differently and looks odd compared to the Rorschach we know in the present. There's something very human about him that adds a quiet tragedy to the man we know now.
Happened several times to the Skrull impostor(s) posing as Hank Pym during the Secret Invasion. Apparently a side-effect of the enhanced shape shifting they were using to escape detection. One issue revealed that they went through no less than 4 different Skrulls who EACH KEPT TRYING TO DEFECT once they settled into the role.
The Vertigo version of Human Target written by Peter Milligan was all about this. The main character, Christopher Chance, was so good at imitating the people he was meant to protect that he needed post-hypnotic triggers to resume his "normal" personality. This problem largely presents itself when he's not in contact with the person he's impersonating, and especially when that person is dead. In the most advanced cases, he has literally forgotten that he was ever Christoper Chance.
Christopher's protégé Tom McFadden actually has it even worse; he wasn't psychologically prepared for the kind of work they do, and has taken to constantly constructing new identities that he disappears into completely because he has no "real" personality anymore.
Marvel's first Captain Marvel was a Kree soldier named Mar-vell, who came to Earth to spy out humanity. He eventually came over to Earth's side for real.
Magica De Spell goes through this in the Donald Duck story "Date with a Munchkin" by Kari Korhonen, where she kidnaps Daisy Duck and takes her place in order to get close to Scrooge McDuck's Number One Dime. During her time as Daisy, she receives Donald's affection for Daisy and takes a liking to their romance. (It helps that she's accidentally also dosed herself with the Love Potion she's using to forestall Donald's suspicions.) It culminates in a Duckburg ball where Magica originally intended to steal the dime, but chooses not to leave Donald's side. However, Daisy has escaped her restraints and crashes the ball, confronting Magica. When Donald takes Magica's side, believing that she's the real Daisy, Magica ends her illusion and flees the scene rather than break Daisy's heart. She later reflects that although she didn't manage the theft, she has experienced "a new feeling," and maybe that's worth something.
Magica manages it again in "A Gal For Gladstone": she hexes away Gladstone Gander's luck so he'll have to work for Uncle Scrooge, then disguises herself as a wholesome girl and seduces him to get close to the dime. She's genuinely touched by his devotion, though, and ends up giving up her chance at the dime in order to save his life.
Punch/Counterpunch in Dreamwave's Transformers Generation One comics. Punch is an Autobot spy sent deep undercover into the Decepticon ranks as counterintelligence expert Counterpunch. However, in developing Counterpunch's "character" and establishing him as a dedicated Decepticon, Punch may have caused an entirely new personality to develop within him; Lately, he's been having blackouts as Counterpunch and is unable to account for his whereabouts or activities, though he suspects Counterpunch is asserting himself and doing his job.
The Silver AgeSuperman had a story in which Clark Kent tries to prevent the demolition of his old home. Pete Ross assumes it's because he's afraid the workers will find something that'll give away his secret identity, but it's really because of Supes' sentimentality. Pete's last line is pretty much the trope. (Remember, this is when writers had decided that Superman was the "real" identity and Clark Kent a mere disposable mask.)
V from V for Vendetta. Who he is under the mask is unimportant, as the mask is a symbol of what he truly is.
In Silver and Bronze AgeSuperman comics, Lex Luthor initially only helped an alien race rebuild its civilization in order to gain their cooperation—but when they hailed him as a hero (even renaming their planet Lexor!), he realized he liked being considered a good guy. Lexor became his home away from home for years, until he himself accidentally destroyed the planet in a fight with Supes. This tragedy caused a major Villainous Breakdown.
Captain Atom was originally a government agent pretending to be a superhero so as to spy on the Justice League. Eventually he found himself becoming a superhero for real, leading to his Crowning Moment Of Awesome, seen here.
In the Fantastic Four story "This Man, This Monster," an unnamed scientist steals Ben Grimm's appearance, voice, and power in order to kill Reed Richards, whom he both envies and considers motivated solely by glory. However, in the course of working with him on a dangerous research project, the scientist becomes so convinced of Richards' selflessness that he sacrifices himself to save his life.
An Affectionate Parody of this story, "And Men Shall Call Him...Hero" from Doom Patrol, has a villain steal Cliff Steele's robotic body in order to kill his Doom Patrol teammates, only to feel unexpected compassion when a lost, frightened blind girl instinctively clings to him. As a result, he sacrifices himself in order to prevent the Omnicidal Maniac Celestius from absorbing her life energy.
Gentle Giant Vathek from the original W.I.T.C.H. comic begins as a villain, but is sent by Cedric to act as a The Mole among the rebels. Vathek, however, decides that Good Feels Good and ends up genuinely changing sides. (In the cartoon Vathek has a smaller role and acts as The Mole among the bad guys while being genuinely on the side of good all along.)
On the one hand, Wally Squad Judges face a constant mental battle to avoid either becoming the criminals they're supposed to be undermining, or simply thinking too much like a normal human being. Many fail; at present, Dirty Frank is right on the precipice.
On the other end, Serial Killer PJ Maybe stole the identity of Byron Ambrose, a wealthy philanthropist, and got himself elected Mayor of Mega-City One. In order to keep up the charade, he had to do as many good deeds as were possible for the mayor - and during this time, he gradually came to enjoy being good so much that he risked his own life and reputation in attempting to assassinate Martin Sinfield for no other reason than that he felt it was for the good of the city. (Sure, he may randomly kill people for fun, but he was still the best mayor Mega-City One has ever had... which speaks for the city).
A long running plot-point of Strangers in Paradise was the "Parker Girl" operation, women who would assume long-term, deep-cover identities and get involved with influential men in order to manipulate politics from behind the scenes. However, when the operation collapsed after the death of Darcy Parker many Parker Girls were trapped in their cover identities, unable to extricate themselves from the lives they had established. In Echo, the next series written by author Terry Morre, there is a crossover with SiP as a character makes contact with some of the women still living their cover identities. Lieutenant Laura Higgs, who used be a Parker Girl named Stephanie who was infiltrating the US Military, asserts that she has a life now and refuses to give up the world she has built. "Stephanie's dead. I'm Laura Higgs now."
In Classic Star Wars, a set of Star Wars newspaper strips, Vader once hires an actor to pretend to be Obi-Wan in order to lure Luke into a trap. The thing was, the actor was moved◊ by how Luke respected him, and started having thoughts like "What would the real Obi-Wan do?◊" He still led Luke into the trap, but then sprung it, dying himself. From Luke's utter lack of reaction◊ before the panel at the top of the page, it's a little ambiguous whether Luke was really oblivious about what was going on.
In Transformers: More than Meets the Eye this happened to Minimus Ambus, the current holder of the title of "Ultra Magnus". Originally a mere soldier in the Autobot army, he had long admired Ultra Magnus, for being the epitome of law and order, and aspired to be a lawman just like him. When the former holder of the title died, and Ambus was offered the chance to actually become his idol by Chief Justice Tyrest, he leapt at the opportunity, throwing himself completely into the role. He's briefly forced to take the mask off during the Remain in Light storyline when Tyrest takes away the Magnus armor and replaces Ambus with his new Enforcer Star Saber, but when he learns that the now insane Tyrest plans to use the Universal Killswitch to kill all Cybertronians who were constructed cold, Ambus announces that Ultra Magnus would never stand for that, and turns against his former boss. By the end of the storyline, he has once again become Ultra Magnus, and is even told by Ratchet that he is the true Ultra Magnus.
The Reveal in the middle of Chapter 3 of the Axis Powers Hetalia fanfic Finding Freedom. You thought that the Beta Couple's main reason for being added in the previous chapter was to give the other main character a boyfriend too or to be the cute established couple? Think again.
"Don't be stupid, although I know you can't help that. Kiku's...not my type."
Also a lie, Heracles told himself. He definitely felt something for the other man, cherished his time with him and his quirks and just... all that made him who he was. When he kissed him, it was real. By now, everything he did with Kiku was real.
Explored in the Mass Effect/Terminator crossover Drift, where Cameron has spent a couple hundred years carefully developing an entire personality construct based on her "Allison" memories, effectively becoming an otherwise indistinguishable human. It turns out that Cameron has apparently been using the Allison persona for so long that elements of her have influenced other parts of her "brain," like her combat programs - which she finds quite troubling, because she is apparently unable to actually do physical maintenance on her processors.
In Deep Cover, a Naruto fanfic. Naruto gets sent on a mission to infiltrate the Sound village, with the idea that his behavior is so loud and obvious that nobody would suspect him hiding something. He betrays Konoha and has a romantic moment with Tayuya while watching it burn. Thinking back on how he made his decision, he realizes that at some point in the past he stopped caring about Konoha and decided that Sound was his home.
Really, almost any Naruto fanfic that has the word 'mask' in the title.
White Rain has Itachi Uchiha and Lucia van Alstyne; the former's motivations were only revealed long after his death, while the latter only came to realize it after being interviewed by Ibiki.
This trope is a major part of the Teen Titans fanfic Avatar. As far as Robin's concerned, when the mask goes on he is Robin - Tim Drake (unusually for a Teen Titans fic, Robin is the Tim Drake version rather than the Dick Grayson one) doesn't exist. He deliberately wears the mask at all times, even when hanging out with the other Titans, because he considers leading the Titans a 24/7/365 job, so decided to simply stop being Tim, who he feels doesn't have what it takes to be a hero.
The Monsters, Inc. fanfiction Angelas Pet Monster involves Randall getting adopted by a human girl. At first, he doesn't care much for her, only wanting food and warmth. However, he quickly grows to like her, which leads to his Heel-Face Turn.
In the My Little Pony: Friendship Is Magic fanfic Without A Hive, by Phoenix_Dragon, a novice ChangelingInfiltrator named Nictis is cut off from his Hive, and forced to pretend to be a (female) Pony named Meadow Song for many, many years, during which it has no contact with his own kind. As the years pass, the identity of Meadow becomes all too real, causing a slow change in Nictis's own loyalties and values.
In Diaries of a Madman, Bon Bon has been away from the changeling hive and amongst ponies for so long that she's come to consider herself as a pony foremost.
Film - Animated
In The Lion King II: Simba's Pride, Kovu is sent to ingratiate himself into Simba's pride in order to kill him. Unfortunately for his mother, Kovu's growing love for Kiara allows him to break free of his mother's conditioning, realize the evil that he is collaborating in and decide he wants no part of it.
Experiment 626/Stitch in Lilo & Stitch. He starts out masquerading as a dog for protection, but eventually Lilo's love causes him to do a Heel-Face Turn.
Diego in Ice Age. He is supposed to get the baby and bring it to the Big Bad, but eventually becomes its protector.
Despicable Me has Gru pretending to be the three orphans' adoptive parent. However, he rescues the three kids from Vector and keeps that role.
Megamind has this, but it's a subversion. He begins to like Roxanne while dating her as Bernard so much that he doesn't want to be a villain anymore. However, after Roxanne dumps him after finding out his identity, it's back to being a villain for him.
But when Roxanne tells him she needs him, while Titan has her tied up on top of a skyscraper, he flips to "hero" mode again and stays that way.
The danger of the unicorn's human guise in The Last Unicorn. Amalthea, the eponymous unicorn, slowly forgets who she was, as she becomes more and more human. It takes the three others protagonists (including the human she fell in love with) to put her back on her quest.
In Treasure Planet, Silver ends up developing a bond with Jim Hawkins, despite him and his crew being the mole and simply being on the ship to steal the treasure. This serves as one of the primary conflicts of the story.
Film - Live Action
Pretty much the entire plot of the Kevin Costner film The Postman. In a post-apocalyptic America where civilization has collapsed, Costner plays a wandering con man who poses as a postal worker of the fictional 'Restored United States of America' to deceive people into giving him food, shelter, and protection. In the process, he proceeds from pretending to deliver the mail to actually delivering the mail, and things sort of snowball from there until he eventually, entirely by accident, ends up basically creating the Restored United States of America he claimed to represent and becoming a postal worker for it.
The whole point of the Charlie Sheen film Beyond the Law, which in turn is based on several real stories about law enforcement agents who pretend to be outlaw bikers to observe the clubs engaging in illegal activities only to realize they feel more at home as outlaws than as cops.
This is more or less the entire plot of James Cameron's Avatar. The main character, who is "piloting"/"possessing" an custom-made alien body for the purpose of infiltration, even remarks in the film at one point that the situation had become reversed - "out there was reality, and in here [in his human body] was the dream." At the end of the movie, he undergoes a ceremony that permanently puts him in the avatar body, and he leaves his old human body to die in the toxic atmosphere.
The plot of Kagemusha by Akira Kurosawa. A lower-class criminal is taught to impersonate a dying warlord as a kagemusha (shadow warrior) in order to dissuade opposing lords from attacking the newly vulnerable clan. He becomes more and more convincing after the death of the warlord, but he is revealed as in impostor after he is rejected by the horse of the warrior. However he chooses a death on battle, in a desperate search for identity.
There are a number of stories in which the main characters pose as heroes, only to actually become real heroes by the end.
The main characters of ¡Three Amigos! are stars of many movies within a movie. A small Mexican village mistakes their movies for a truthful account of actual heroes, and hires them to save the town from bandits, while theymistake the offer for an offer to simply put on a show. Unfortunately, having lost their jobs, they have no place to go to after learning the truth, so they decide to save the village anyway, becoming the very movie characters they played.
The main point of Wedding Crashers; this one using the "fall in love" variety with both protagonists. Things go south when they're discovered, but they manage to work out a happy ending.
Occurs for the worse in Mean Girls: Naïve Newcomer Cady joins the popular girls' clique only because her friends want her to get inside information on Queen Bee Regina so that they can knock her several pegs down the social ladder. Cady succeeds in doing this, but her experience as one of the "Plastics" causes her to become as shallow and popularity-obsessed as them, and she takes over Regina's former position. Fortunately, when she realizes what she's become (and has a Fallen Princess experience), she snaps out of it and makes amends.
A variant appears in Dave: an actor who bears an uncanny resemblance to the President of the United States is hired by advisors to stand-in at an official function whilst the real President is seducing his secretary. Unfortunately, the President suffers a stroke during the act and is rendered non-responsive, forcing the actor to remain in the role indefinitely; he ends up becoming a more noble and honest President than the actual one, and falls in love with the First Lady.
Alice in Anti Trust was originally hired to be The Mole, but ends up falling for the protagonist and refuses to betray him.
This is the main character problem affecting Robert Downey Jr.'s character in Tropic Thunder. Specifically, he's supposed to be an Affectionate Parody of Daniel Day-Lewis.
Inverted in the first Darkman movie. When Darkman interacts with his girlfriend Julie after nearly having been burned to death, he makes good use of his artificial skin to pretend to be the same Payton Westlake he always was. However, at the end of the movie, when the Big Bad has been defeated and Julie finally sees Darkman's face as it truly is, she tries to reassure him by telling him that she can still love him despite his horrible injuries. Darkman replies that their former relationship could never go on because, while he was wearing the mask of the old Payton (among other masks), the man behind the mask had changed into an altogether different person.
This was the plot of the James Bond movie From Russia with Love; the Bond Girl was sent by SPECTRE (under the guise of SMERSH) to seduce him into a trap. She pretends to be a Russian cypher clerk who's fallen in love with Bond's picture, only to fall for him for real.
In While You Were Sleeping, Lucy saves the life of the man she has a crush on and, due to a mistake at the hospital is assumed by the staff — and the man's family — to be his fiancée, whom they haven't met. A variation, however, in that Lucy isn't a villain with malicious intent; she's initially mortified by the error and tries to clear it up right away, but finds the man's warm, welcoming and immediately accepting family, in contrast to her own painfully lonely life and lack of family, a bit too hard to give up. Then she falls in love with his brother — right before the man comes out of his coma and, due to what-he-thinks-is-amnesia, is convinced that she is his fiancée...
A variation occurs in the Woody Allen movie Zelig: the protagonist becomes the mask involuntarily, taking on the traits of whoever is around him, be they Nazis, pilots, or Greeks.
Undercover Brother has Brother become Anton Jackson to infiltrate The Man's company. He becomes the mask due to mayonnaise and the White She-Devil. When he returns to normal, the White She-Devil goes through a similar transformation and does a Heel-Face Turn.
The Assignment (1997). The protagonist, a naval officer with an uncanny resemblance to Carlos the Jackal, begins to take on the nature of the violent, charismatic terrorist after being trained to copy his methodology (as part of a plot to frame Carlos as a CIA informant so he'll be murdered by the KGB). The final scene shows him going to burn a spider with his cigarette as Carlos did in the opening scene, but he stops at the last second.
Total Recall (1990) (1990) Does this quite literally (or does it?) - Our protagonist Doug Quaid is told that his true identity is actually Hauser, Cohaagen's evil sidekick: but Quaid has other ideas. As Cohaagen puts it: "I didn't want it to end this way, I wanted Hauser back, but no... you had to be Quaid!"
Pretty much the point of Donnie Brasco, where Johnny Depp's character, an undercover cop, develops a friendship with his primary mob contact and feels guilty about betraying him.
Heavily discussed in The Departed by Costigan, where he worries that the horrible things he has to do while undercover are actually making him more of a horrible person, which culminates in him being unable to trust the police department at all; he asks to resign rather than be reinstated after Costello's death ends his mission, and upon realizing that Sullivan is a mole he immediately goes rogue to try to deal with him rather than even considering reporting him to anyone else in the department.
The main source of drama in Infernal Affairs, the Cantonese film The Departed is based on, was the psychological impact of the main characters' double lives as Andy Lau's character wishes to become his mask while Tony Leung Chiu-Wai's character fears he is becoming his.He eventually goes so far as to kill everybody who knew his real identity and could incriminate him, with the exception of his wife.
In Troop Beverly Hills we get Annie, who was sent to the title troop by Velma to to discredit their leader and get the troop disbanded. Eventually she grows a spine and gives up on the pursuit. Of course, Velma catches on to this and tries to fire her before the climactic final competition.
In Who Framed Roger Rabbit, according to a comic book sequel, this is the origin of Judge Doom, who was originally a Toon specializing in villain parts and changing his appearance for every short, akin to a Toon Lon Chaney. After a grenade accident, the actor part of the "Actor playing a villain" slowly vanished and he never appeared out of costume/make-up, to the point that no one in Hollywood could remember what he looked like.
In the film version of V for Vendetta, Gordon Dietrich reveals to Evey that he not only keeps a ton of contraband art, religious items, and other memorabilia in a secret room, he also has a predilection for certain government-unfriendly sexual appetites. Or rather, he had these appetites before years of having to pretend he didn't . . .
Gordon: "You wear a mask for so long, you forget who you were beneath it."
In Batman Begins, Rachel is the one to point out Bruce is the mask, and that the man who was once Bruce Wayne has become the Batman, wearing Bruce Wayne's face as an alter ego. Alfred warns Bruce of it earlier in the movie:
Alfred: You're getting lost inside this monster of yours.
The father of the title Lord of War was a Ukrainian who, along with his family, emigrated from the Soviet Union to America under the pretense of being Jewish. He would later on fully embrace the Jewish lifestyle, opening a store with the Star of David as part of the logo, faithfully attending synagogue services, and even obeying orthodox Jewish dietary laws, much to the annoyance of his Catholic wife.
Anatoly Orlov: I'm going to temple.
Irina Orlov: You're not going to temple! You go to temple more than the Rabbi!
In Plunkett And Macleane, Macleane infiltrates the rich upper classes so he can rob them blind with his fellow highwayman. However he begins growing too fond of acting like he's rich and squandering money on his gambling habits.
Subverted in Cypher when Morgan Sullivan's spy alter ego that he created for himself is ignored when Digicorp transplant him into his new identity by way of brainwashing. The next plot segment is driven by his annoyance that his new persona doesn't smoke or drink whisky. Also inverted: The spy alter ego was his true personality re-asserting itself, Morgan Sullivan was the mask he was unbecoming.
This is the plot of Sister Act when Whoopi Goldberg's character becomes a nun. Whoopi comes to like the nuns and their work to help people in need, but she also convinces them to serve the Lord with more joy and less woe, singing passionately.
Smokin' Aces features an interesting inversion of this: after FBI Agent Freeman Heller goes undercover as Mafia Hitman Primo Sparazza, the higher-ups at the FBI became wrongfully convinced that he had become the mask, and tried to have him murdered. Heller survived the assassination, and to retaliate against the Bureau that betrayed him, really did become the mask, eventually becoming the head Mafia Don.
A classic movie example is Humphrey Bogart's character in The Left Hand of God. He plays a mercenary in China who uses the identity of a dead priest to escape his warlord employer but that means actually acting the part of a priest at a medical mission. Luckily he's a Catholic boy so he knows the drill. He also does his best to live up to the part with predictable results.
Point Break stars Keanu Reeves as an FBI agent who goes undercover as a surfer to get close to a suspected bank robber. The inevitable occurs.
Jill in The Whole Nine Yards. She was hired by Oz's wife to kill him, so she started working as his assistant, to get closer to him. She ended up liking Oz so much she couldn't go through with it, and just kept on working for him.
Ronald Colman won his only Academy Award for doing this in A Double Life. He plays a Shakespearean stage star who is something of a method actor, immersing in and "becoming" each role. Already having (actual, but unfounded) concerns about his wife's fidelity, he then gets cast as Othello...
Kayla Silverfox in X-Men Origins: Wolverine is blackmailed by Stryker into posing as Wolverine's lover. However, near the end, the mask has become real.
Done to the letter in The Baker, a British comedy about an assassin with second thoughts about his profession who escapes to a tiny Welsh town and poses as the local baker to avoid attention. Turns out, he likes baking a lot more than he does killing, and a local girl captures his attention. Sure enough, he ends up as the town's baker, and gets the girl.
In The Wild Hunt, Murtagh and his fellow Celts start playing their LARP characters for real, with bloody consequences.
Kichi's mother begins to worry that this has literally happened to her after she dons a demonic mask in an attempt to scare her daughter straight in Onibaba.
Big Daddy: Sonny Koufax adopts a five-year-old boy and lies about being the kid's biological father for the completely self-serving motive of gaining respect from certain people who have criticized him for not acting his age. But he gradually comes to really love the boy, even after one part of his grand plan fails.
The original Fright Night features washed-up horror actor Peter Vincent becoming a real vampire-hunter, and gradually growing into the role.
Barbara "Down with Love" Novak is a best selling author who tells women that they don't need a man to be satisfied as women. It turns out there is no Barbra Novak and her real name is Nancy Brown. She has been pretending to be Barbara Novak to get Catcher Block to fall in love with her but what she didn't count on was by pretending to be Barbara Novak... she would actually "become" Barbara Novak.
Al Di La Della Legge is about a bandit, called Cudlip, who initially becomes the sheriff of a town for his ulterior purposes but gradually grows into the role, to the point where he and his new friend, a European immigrant called Novak, kill his two partners when they try to kill Novak in an attempt to steal the gold. The film ends with him holding and looking at his badge as Novak tells him he's earned it.
The first Addams Family movie has Gordon Craver, son of the film's antagonist, impersonating Uncle Fester to discover their fortune. He eventually starts settling in with the family and appreciating their strangeness. It turns out to be inverted, since Gordon actually is Fester with amnesia and was taken in by said antagonist.
The Chevy Chase comedy Funny Farm has his character Andy and his wife Elizabeth moving to a small town in the country, but the odd behavior of everyone there and some personal troubles between the two lead to them to having a falling out, wanting to divorce, and hoping to both move away as soon as possible. They work together with all the inhabitants to lure in another couple into buying their house under the prospect that town is the perfect place to live in and that they are Happily Married. As they maintain the charade though Andy and Elizabeth realize that in spite of everything that's happened they still love each other and actually do love living in the town.
Training Day: One Epileptic Tree claims that Alonzo is so dangerous precisely because being "The Wolf" does not come naturally to him - his bad guy persona is taken to the max precisely because he has to construct it.
In Legend Of The Black Scorpion, Wu Luan and Wan have a discussion about the power of masks in theater and whether or not wearing one brings about a greater performance. This as Wan is slowly becoming one with her queenly mask.
In The Unknown, Alonzo the Armless really becomes armless. He decides to go with it when Cojo laughingly remarks that he forgot he has hands when he lights a cigarette with his feet.
The East: Sarah, a corporate intelligence agent, infiltrates a bunch of eco-terrorists. Her boss tells her that a certain amount of this trope is to be expected in any long-term undercover assignment, but she goes just about all the way in.
Back to the Future Part III: After accidentally being sent to 1885 towards the end of Part II, Doc tells Marty in his letter that he'd set himself up as a blacksmith as a cover while attempting to fix the time machine. But when he realized the damage was beyond the capacity of 1885 technology, he buried the time machine so that Marty could fix it with the help of his 1955 counterpart and go back to 1985 himself, and accepted his place as a blacksmith, content to stay in 1885.
The Impairment features two examples of this Meleeo and Allie Parker and both are an interesting contrast from one another. Whereas Allie Parker, the human, dons a monster suit of which she commits murders on Mildwood University and grows to believe herself to be a "mother" of sorts to the Nytera, the creatures running amuck at night, Meleeo, the alien, adapts to life on campus in the form of a mild mannered human college teacher named Norman Oswald and plays the role of a helpful mentor to students, including Kyle and Mark especially.
In the Boundary's Fall series, Katya is one of many agents sent to infiltrate Alrendria by Tylor Durange to act as spies and, if need be, assassins. She falls in love with Dahr but continues to pass along information until a critical moment, when Jeran, who has figured out the secret, has himself handed over to Tylor as a diversion so that Prince Martyn can escape. Manages to combine both the My God, What Have I Done? and the Heel-Face Turn options.
There's an intereseting variation of this trope in the Warrior Cats series. It turns out that Scourge was a product of this, but in the reverse of the norm: See, when he was little, he was tricked into running away from his home and happened to end up in the city. To survive, he managed to fool the other rogues residing there into believing that he was a cold-blooded killer so they would fear him and bring him free food. However, by the time he actually kills someone, he slowly starts to become the unfeeling, cold-blooded monster he was portrayed as in his debut.
In Henri Duvernois short story "Clothes make the man", a trio of thieves has one member wear a police uniform as part of their plan. At first he doesn't like it, but after being treated like a cop he 'arrests' his fellow thieves.
In Good Omens it's repeatedly pointed out by other demons that this seems to be what happened to Crowley; he's spent so much time making sure he fit seamlessly into the role of the human he's supposed to be that he became that person over time, and eventually comes to really love humanity. Aziraphale does this as well, integrating into humanity well enough that he becomes enough of a bastard for Crowley to spend several millennia with.
Likewise, at one point, Adam the young Anti-Christ is sent a massive Hellhound which takes the form of small yapping dog as a disguise. It grows to enjoy its new form and carefree life of catching sticks more than it ever enjoyed chewing up the souls of the damned and such. The presence of female dogs probably didn't hurt much.
Yes and no with the hellhound. While the dog definately DID prefer Earth to hell in the end, the reason he took the smaller form wasn't as a disguise but because whatever the Anti-Christ named him, would define him and Adam chose the name 'Dog'. So he became the perfect embodiment of a dog, changing him from the very start.
The plot of The Assassins of Tamurin centers around the Femme Fatale protagonist realizing that, contrary to what the Cult she's grown up in has taught her, she's been on the wrong side. Not only does she really fall in love with the king she's been spying on, she believes his plans, not The Chessmaster's, are best for the kingdom.
In Aaron Allston's Wraith Squadron books of the Star Wars Expanded Universe, former Imperial Intelligence agent Gara Petothel fits this trope to a "T". She infiltrates Wraith Squadron as Lara Notsil, but soon finds that Good Feels Good and she prefers her Rebel identity. She even falls in love with fellow pilot Myn Donos, the Sole Survivor of a squadron her information work helped destroy! She gets to declare her love before her identity as The Mole is exposed, and even with everyone believing her to be an Imperial, she still goes on to do the right thing and bring down Zsinj. Afterward she adopts her old training persona of Kirney Slane and settles down with Myn.
Another example, from some older comics: Darth Vader hires an actor to act as Obi-Wan to lure Luke into a trap, but the actor starts to see why Luke admires the figure he acted as so much, culminating in a Heroic Sacrifice.
The Hand of Thrawn Duology has the Devist family, a number of clones of Soontir Fel who kept together and secretive to avoid the Fantastic Racism that comes with being a clone. They were set up as a cell of sleeper agents, supposed to answer the call when the Empire needed them, and in the mean time they became farmers. But like Soontir before them, they loved the soil, and loved it more than the Empire. When they scramble in their TIE interceptors and save Han and Leia, they don't report them, and are eventually talked into helping the New Republic with the Camaasi Document crisis.
Fel himself states that they and the other cells were designed to do this — to develop stronger loyalty to each other and their world than to the Empire that quite literally created them. This way, when a threat came past the galaxy's edge, they would be able to fight it without too much worry about ideological ties. Pity the villains dug most of the cells up to act as cannon fodder well before that...
Luke Skywalker and the Shadows of Mindor has Luke half-awake during an eternity after the heat death of the universe, after all the stars have burned out. He escapes the projection of this eternity before he can despair enough to let his body be stolen, but for quite some time later he's cynical, depressed, even nihilistic, believing that all of his friends are using him and nothing will matter in the end. He's Luke Skywalker, so he very consciously decides to act exactly like he would have before going through that, hoping that eventually it will stop being an act and he can "fall back into the dream of the light". Fortunately he doesn't have to wait that long before regaining his faith during a Mind Screwy metaphor-heavy sequence.
Luke seems particularly prone to this trope. It's the only thing anyone remembers about Dark Empire. That and the Emperor's clones.
Lowbacca in Diversity Alliance. He isn't racist, but he can see where the Alliance gets their ideas from. Even though they're basically the Flanderized version of the Black Panthers.
Robert A. Heinlein's Double Star is about an actor who is hired to impersonate a kidnapped politician so that an election won't be disrupted. As time goes on the job gets stretched longer and longer and then the politician dies, with the masquerade still in place. He has to keep up the impersonation for over 25 years, and pretty much becomes his role. (He was an anti-Martian before the job, and is hired to impersonate one of the biggest pro-Martian activists. By the end of the 25 years, he has completed all the causes of the politician, and more.)
In C. J. Cherryh's Foreigner series, a wandering starship's crew are marooned on a planet of nine-foot-tall humanoid aliens, called 'atevi'. Unable to understand human emotions or the idea of love and friendship, they went to war against the perceived threat to their way of life. Human annihilation was only prevented by scholars on both sides equating the "English" (or should that be Basic?) word for treaty, with man'chi, the ateva word for association, a hard-wired homing instinct under fire. Since then, humans live on the island of Mospheira and the atevi of the Western association remain on the continent. No one is allowed to make contact between the two except the interpreter, or 'paidhi'. Bren Cameron becomes so attuned to atevi mindsets and language that he eventually becomes aligned with their point of view and begins to lose human feeling. He cannot show any form of emotion, because that would be deemed extremely threatening by atevi, whose legal recourse in disputes is assassination via an Assassins' Guild. He gradually takes on their mannerisms and can no longer remove the bland, impassive expression on his face - literally becoming the "mask" that he has to wear in public on the mainland.
In the little known sequel to The Prisoner of Zenda, Rupert of Hentzau, the protagonist who had impersonated the King of Ruritania in the first book finds himself forced to masquerade on a permanent basis in the sequel although he is assassinated shortly after this happens.
Occurs in reverse in C. S. LewisThe Great Divorce. A man who keeps trying to impress his love interest slowly becomes "The Tragedian", a false personality given to hackneyed dramatic gestures, and his real, honest (if average) personality gradually shrinks away to nothing. Ironically, she loved him as he was.
Moist Von Lipwig in Going Postal intially only pretends to like his new post but ultimately gets his criminal thrills by being a Large Ham showman for the post office.
As we see later in Making Money, though on the surface he seemed to embrace his new job, his criminal's instincts have never left, and he becomes more and more dissatisfied with it as time goes on. His criminal instincts remain, but he acquires a strong drive to use them for good. (He was a sort of Anti-Villain before, but has definitely graduated to Loveable Rogue over the course of his new career).
In Monstrous RegimentSergeant Jackrum. Not only has she been in disguise long enough to make a detailed account of every other female hiding in the ranks of the army, she also has evaded her service papers discharging her from the army for years. As the war ends, she admits to Polly that she doesn't want to return home to just be an old biddy. Polly suggests that she keep the mask and return home as a respected retired sergeant instead.
From the same book, The command staff who became just as eager to punish women, as Jackrum eventually warns Polly to avoid the same pitfall.
The Auditor from Thief of Time who becomes Lady Myria. In fact, a lot of the Auditors who take on human form start to act gradually more and more human. Lady Myria is just the only one to make a genuine Heel-Face Turn.
Older than Television: Max Beerbohm's The Happy Hypocrite (1896) features a literal mask to hide the signs of dissipation in the villain's face; when the villainess realizes the truth and pulls off the mask, the face beneath has literally been molded into the mask's form.
In the series Instrumentalities of the Night, by Glen Cook, protagonist Else Tage is sent on a mission to spy on the west for the kingdom of Dreangor (i.e., Muslim Egypt). Pushed along by the fact that the Evil Chancellor responsible for sending him on the mission is trying to have him killed, he starts questioning his loyalty. This process is clearly indicated by the fact that after spending the first book referring to him as Else, the narration switches to calling him by the pseudonym he's using.
Kurt Vonnegut's novel Mother Night is about an American who moved to Germany and was later hired to spy on the Nazis. While never consciously converting to Nazism the main character is eventually held for being a Nazi war criminal. The character himself is actually unsure of which side he belongs to. The introduction of the novel lampshades the theme when it says "We are what we pretend to be."
The story is An Aesop about the fact that what you do is more important than what you believe. You are good or evil based on your acts, not whether or not you think you are good or evil. As for the protagonist, he was asked to become a Nazi by an American agent and the information he provided the Allies throughout the war was of great help. The problem he has is illustrated when near the end of the war a Nazi friend tells him he knew the protagonist was a spy but never reported him because whatever damage he did as a spy would be more than offset by the help he was giving the Nazis in his cover role. Obviously, that would bother any anti-Nazi person, which he was.
Cat's Cradle, by the same author, has a religion created by two men to keep a country happy. They decide to have the religion outlawed, with one playing the role of President, the other Messianic Archetype. Eventually, of course, the President gets too deep into his role and starts executing heretics.
In the Vorkosigan Saga, Miles Naismith Vorkosigan finds himself becoming Admiral Naismith (his fictional identity) more and more, and Lord Vorkosigan, his actual identity, less and less. This is helped by the fact that the reason he created and maintained his fictional identity was to have an outlet for the drives and urges his true identity is not permitted to indulge in. However, Memory happens and Miles finds his alter ego destroyed — and he realizes that after everything else has been stripped away, he's still a Dendarii hillman in his bones. In other words, his Naismith persona had to always succeed, but his Vorkosigan persona simply didn't know how to lose. Miles successfully adjusts by finally allowing his true identity to fulfill the impulses his alter ego had been satisfying, though his mother claims she thought he'd flee Barrayar and "choose the little admiral".
And his clone, Mark, was brainwashed and trained from birth to impersonate Miles, and after breaking free of his captors he struggles for years to find his own personality and avoid Becoming the Mask.
Also, Sergeant (then Armsman) Bothari becomes whoever his commanding officers need him to be. Torturer (for Ges Vorrutyer). Soldier (for Admiral Lord Aral Vorkosigan). Bodyguard (to Miles). Cordelia thinks of him as a hero, so he makes himself one for her.
Agatha Christie pulled this one with Dr Rathbone from They Came to Baghdad: a con man who established a philanthropic society to make money, but ended up believing in what he preached.
G. K. Chesterton's book The Man Who Was Thursday has a character who was an actor that portrayed an anarchist philosopher as a joke, and did such a good job of it that he convinced everyone watching that he really was the philosopher and even bested the philosopher himself in a debate, resulting in the real philosopher getting tossed out into the street. He is then forced to continue playing his role, even when he was elected to the Council of Days. By the time he meets the protagonist, he's been playing the part of an old man for so long that he can't stop.
In Ender’s Game, Valentine starts to worry about adopting "Demosthenes's" more radical, hard-line opinions after writing too many columns under that name. (Whether Peter is similarly worried about becoming "Locke" is unknown.) She uses that as the basis of another article - that people who give in to the Warsaw Pact will end up giving up everything (note that there's some historical evidence for this idea - just ask Neville Chamberlain).
Whether Peter is worried about the possibility, this occurs to him throughout the Shadow series. Contrasting the sadistic boy in Ender's Game to the non-aggressive Hegemon in Shadow of a Giant displays how Locke's persona changes Peter Wiggin.
Valentine: Perhaps it is impossible to wear an identity without becoming who we pretend to be.
In Star Wars, Boba Fett occasionally mentions that this is how he became the bounty hunter he is, by working out how a hunter "should" act and sticking with it until it became second nature. Understandably, it wasn't very good for his social skills.
In Outcaste, first of the Spaceforce novels, the protagonist Jay is born into a world where everyone's occupation is absolutely determined by birth, or 'caste'. Dissatisfied with his fate as a lowly blacksmith, Jay sheds his identity and masquerades first as Priest Caste, and then as Swordbearer Caste. He spends many years as a swordbearer, is evidently comfortable with this identity, and presumably would have lived the rest of his life like this if events hadn't conspired against him.
The title character of Montmorency starts out as a thief in the Victorian era, who concocts an upper-class identity so he can fully savor the profits of his crimes. Eventually, he finds life as a respectable gentleman so satisfying that he goes legit, retiring the original thief-persona he's grown ashamed of, and anonymously making amends for his crimes.
In The Dresden Files, as revealed in Changes, Martin becomes this. He was initially sent by the red king to infiltrate the Fellowship of St. Giles, but eventually comes to sympathize with them. Doesn't stop him from eradicating them to achieve his goals, though.
Fidelias in Codex Alera takes a position in the First Aleran legion as the Aquitaines' spy. However, he finds that he rather enjoys being Valiar Marcus, and eventually betrays the Aquitaines to support Tavi, who he has decided would make a better ruler. (The fact that he's the rightful heir is entirely incidental) Even the sections from his perspective tend to refer to him as Valiar Marcus rather than his real name, foreshadowing how absorbed in the role he gets.
This has been noted two times by characters. Marcus/Fidelias chides the outwardly perfect, but incomplete disguise of Gaius Sextus and later by Octavian, when he notes that real difference between Valiar Marcus and Fidelias is not in facial features, but in subtle things like speech patterns and intonations, stances and movement. Also, Fidelias smiles.
Jack London's short story "South of the Slot" features a sociology professor who adopts a working-class persona to write about the culture from a scholarly standpoint, but finds himself spending more and more time as the rowdy labor-hero, until he eventually forsakes his career and impending marriage to become the other persona full-time.
This, sort of, the plot of both his "The Call of the Wild" and "Whitefang." In the former a pampered pet dog is dognapped and becomes first a sled dog and then alpha wolf of a pack of Alaskan wolves; in the latter a wild wolf becomes a beloved pet. These would not really fit except that both stories are essentially told from the first person perspective.
The harried archdemon Mephistopheles mistakenly signs up a medieval cutpurse named Mack the Club for the do-over of the Millenial Contest, thinking him the learned Dr. Faust- And Mack doesn't argue his identity, as he doesn't want to get in trouble with Hell itself for trying to rob the great magician Faust. Mack eventually becomes the historical Faust by being better at being Faust than Faust himself- much to the original's wrath.
In the Anita Blake book Obsidian Butterfly, Anita is extremely concerned that her friend Edward, the sociopathic assassin, has proposed to a woman with two children under the guise of Ted Forrester, his respectable Federal Marshal identity. She quite thoroughly berates him about exactly how he managed to let his personal life get quite so out of control but relents when he manages to show her that he really does love his soon to be family. Of course, this involved Edward as Papa Wolf, Anita as Mama Werebear and a large body count when the bad guys decide it is a good idea to kidnap Edward's soon to be step children even when they know who he is.
Explicitly identified as one of the risks facing the shapeshifting secret agents of Ron Goulart's Chameleon Corps stories. Fearing the loss of his own identity one agent even spent several months as a baboon in an apparent attempt to avoid another assignment.
In The Obernewtyn Chronicles, supporting character Domick becomes a spy and works as a torturer under the name 'Mika'. As Mika, he is much crueler and selfish, to the point that it destroys his relationship with his partner Kella. Later, when he is under mental attack, he flees into his own mind and Mika, who has evolved to become his own personality, takes over.
O. Henry's "A Retrieved Reformation". Master safecracker Jimmy Valentine poses as an ordinary salesman in a town, and becomes the mask to the extent that he gives up his old life and plans to marry the banker's daughter. He even arranges to get rid of his trunk of safecracking tools. And then, on the day he hauls the trunk into town to get rid of it, the one cop who might recognize him shows up hunting him. And a child gets trapped in the bank's vault in such a way that only a master safecracker could possibly get her out before she suffocates.
In the Belisarius Series, Damodara starts as a Reasonable Authority Figure, but after being in command of the honourable and noble Raput army he can't claim everything he does is based on mere practicality about not offending them. Even the Ye-Tai assigned to the army, despite the general opinion of the Ye-Tai on both sides of the conflict as being brutal barbarians, start behaving better, with the resulting increase in respect granted to them.
Fulbert from the post-Apocalypse novel Malevil. He claims to be a priest but almost certainly wasn't one from before World War III. However, after he is seen in action it's revealed that even if he wasn't one before, he's certainly believes himself to be one since adopting the role. Unfortunately for La Roque, there is no change of heart with Fulbert and he is their Sinister Minister, believing his cruelty and harboring Vilmain's marauding army to be punishment from God.
In Eric Ambler's Journey Into Fear, Mathis, a fellow passenger of the protagonist on the eponymous journey, is a French socialist. Towards the end of the book, he reveals that by origin he was from the impoverished fag-end of the French aristocracy and a royalist who was henpecked by his snobbish petite bourgeois wife. After accidentally mortifying her in front of her friends by repeating the opinions expressed at a socialist meeting he attended out of curiosity, he started adopting deliberate public espousal of socialist views whenever she was unreasonably vicious to him. In the course of reading the books and pamphlets he buys to make his arguments more damaging (coupled with his experiences as a combatant in WW1), he comes to believe in the truth of his pretended views and becomes a socialist by conviction (to the extent of being dismissed from his post of the manager of a factory when he supports its striking workers).
In A Song of Ice and Fire, Sansa Stark undergoes this when masquerading as Littlefinger's bastard daughter. She starts thinking of herself as Alayne Stone, her fake name, and refers to Littlefinger as her father, even while he's making sexual advances on her.
This happens to several characters as the story goes on. Before book 4, the title of each chapter is the point-of-view character's real name. Starting in book 4, the titles of most chapters have changed to whatever alias or title the point-of-view character may be using at the moment.
In the James Bond novel Moonraker; Gala Brand, an undercover government agent, is nevertheless passionate about her work as Hugo Drax's security officer.
The Postman: A lone traveler After the End finds a dead postal worker and takes his jacket and clothes for warmth. People he meets treat him like his actually is a postman, which he goes along with because it keeps him fed and sheltered. He eventually becomes an actual Unstoppable Mailman and creates a network of post offices.
One Sesame Street short story had Big Bird pretend to be sick, only to fall sick for real the next day. He does get better by the end of the story, though.
Ignazio Silone's Bread and Wine concerns a Communist fugitive in Fascist Italy who disguises himself as a priest and grows into the role, discovering a version of socialism more consistent with religious faith. In a possible Real Life twist, although Silone's public identity was as a Marxist turned anti-Communist leftist, historians in the 1990s alleged he was an informer for Mussolini's fascist government.
Eleanor Farjeon's "The Kind Farmer" was a Jerk Ass who did some routine courtesy for a poverty-stricken widow who didn't know him. She told the whole town about his kindness and kept hanging around helping him out until he married her. For her sake, he kept up the "kind" facade. When she died in childbirth, he had to go right on being "kind" because of his daughter.
Happens to Vlad Tepes in Count and Countess, who initially just wanted revenge against his father and the Ottoman Empire for the deaths of his brothers. At first his cruel practices (especially the impalement) are meant to psyche out the enemy army, with whom he spent some time as a child, but the more cruelties he undertakes, the more commonplace he finds them.
In The Hunger Games, this occurs when Katniss pretends to be in love with Peeta just to keep them both alive in the arena. At the end of the first she's prepared to kill him to save herself. Contrast the end of the second, where she's totally prepared to die so he can continue living. At the end of Mockingjay, she chooses Peeta over Gale.
There is a Sweet Valley Twins book where the twins invent a triplet named Jennifer and have Jennifer become friends with mean girl Brooke in order to lure her into humiliation. However, the longer Elizabeth stays in the "Jennifer" role, the more she starts to sympathize with Brooke and genuinely wants to be Brooke's friend.
Inverted and played straight in Goosebumps with the Haunted Mask. When Carly Beth wore the mask, she became crueler and more menacing. According to Word of God, the Mask itself only became hideous when the maker covered his own hideous face with it.
In the second half of Addie Pray, the novel whose first half was the basis for the movie Paper Moon, Mose and Addie get recruited to help a crooked lawyer fleece a rich elderly widow by Addie pretending to be her lost granddaughter. Addie (in particular) and Mose decide they like the old lady better than the lawyer.
In one Berenstain Bears book, Mama had grown increasingly annoyed with the family's lack of manners, and as a result, laid down some strict rules on how to have better manners. The cubs didn't like the idea and decided to drive Mama crazy by acting overly polite. It backfired when they began doing it naturally and even call Papa out on name-calling when he insults a driver in front of him toward the end of the book, little realizing (as the driver subsequently explained to him) that they were in front of a duck crossing.
In Star Wars: The Old Republic: Annihilation, Kana Tarrid was a promising Jedi padawan under Jedi Master Gnost-Dural. Even then she was a thrill-seeker less concerned with Jedi code and more concerned with action. In order to better channel her desires, Gnost-Dural sent her to infiltrate the Sith Empire under the guise of a fallen Jedi who wishes to study under Darth Malgus. Naturally, she ends up being corrupted and turns to the Dark Side, changing her name to Darth Karrid and becomning one of the biggest enemies to the Republic after building and commanding the Ascendant Spear, managing to get herself appointed to the Dark Council despite not being human or True Sith.
Legacy of the Dragokin: Zarracka pretends to be Benji's sympathetic 'Auntie Zarracka' to enlist his help in escaping her tailor-made cell. Once she was in the clear she planned on killing him for knowing too much. By that time she's become genuinely fond of him.
In The Witcher books doppelgangers suffer from this (or enjoy this) to a degree. Unlike most examples here this is instant rather than gradually increasing. When disguised they get much the same feelings the original would in the same situation. The one impersonating Geralt knew that Geralt would rather take him alive than kill.
"Mark Twain" from Blonde Bombshell was a probe for the Mk. II bomb, whose posing as a "Dirter" (human) turned from fitting in to becoming one. Lucy Pavlov is revealed to have done the same, as she is the Mk. I.
This happens to Clover Lappina in Spectral Shadows. At first she arrives seeking only social status and money, feigning her love, but slowly...
Taken quite literally in the Star Trek: The Next Generation episode "Masks". Data becomes the embodiment of The Sun, Masaka, wearing her mask. Picard dons her counterpart's mask to "become" Korgano and convince "her" (Data) to sleep and end the ritual.
Ro Laren goes undercover to infiltrate the Maquis near the end of the series, but ends up sympathizing with them so much that she sabotages Captain Picard's plan to draw them out in the open and joins them for real.
In the Deep Space Nine episode "Soldiers of the Empire", a crew of Klingons are demoralized enough to drop their mask and let us see them as ordinary grousing soldiers just like humans. Then at the end they recover enough to put their mask on again and become a Proud Warrior Race.
Deep Space Nine has an episode where Miles O'Brien infiltrates a crime syndicate. While doing that, he forms a genuine friendship with Liam Bilby, a local crime boss. Throughout the episode Miles becomes increasingly conflicted, and ultimately attacks his Star Fleet liaison and tries to warn Bilby that he has been compromised.
In an episode of Star Trek: Voyager, the crew finds out that some con artists are impersonating them. One of them, the fake Tuvok, really gets into the role: he seems to sincerely admire the values of the Federation, and is awestruck when he finally meets his counterpart face to face. The real Tuvok is not impressed.
Fake Tuvok: Logic suggests that neither of us has the advantage.
Tuvok: Your logic is flawed (blinds him with a flashlight).
One episode of Castle deals with this. A con artist dates a rich girl in order to get her money while his partner finds her way in as a servant. The guy falls in love with the rich girl, however, and tries to break off the con. His partner kills him and tries to get away with it, but Castle and Beckett trick her.
In season 2 of Heroes, Mohinder is originally working with HRG to infiltrate the Company, but eventually switches sides and betrays him, joining the Company for good.
It's a popular (if not obligatory) concept in Sylar/Mohinder Fan Fiction that the two became infatuated with each other while Sylar pretended to be Zane during their roadtrip to Montana. Angst ensues.
Sylar receives an involuntary Nathan mask at the end of season 3.
Sharon/Athena in the 2000s Battlestar Galactica is ordered by the Cylons to make Helo fall in love with her and impregnate her. She ends up falling in love with him as well, and defects to the humans. Indeed, she becomes more anti-cylon in her attitudes than many humans.
Later, Boomer, another copy of Number 8 seduces/manipulates Tyrol to get him to help her but she hesitates to go through with it and soon regrets her actions.
Another minor example is Kat whose real name was Sasha. In her previous life, she used to be a drug runner and a smuggler which is where her piloting experience came from. When the Colonies were nuked, she took the name and identity of another woman that she knew was dead and worked herself a fake background and all. By the time her previous life caught up with her in Season 3, she was fully immersed in the identity she built herself.
Sawyer from LOST falls in love with the woman he is conning, and confesses to her that she was being taken advantage of. He then proceeds to carry through with the con and steal her money anyway, albeit with some apparent remorse.
In season three, Juliet was meant to infiltrate the survivors in order to determine whether any of the survivors were pregnant, but by the end of the season she's firmly on the side of the survivors.
Eko was guerrilla who essentially became his priest brother. He temporarily reverted to his former self twice: he killed guerrillas in self-defense in Nigeria, and when he met Ben Linus, he told him about an off screen incident in which he beat two Others to death with a rock.
A short-lived series from the 90's called Legend (starring Richard Dean Anderson and John De Lancie) focuses on a writer in the Old West who creates a popular series of pulp novels featuring a dashing cowboy hero known as Nicodemus Legend. With the help of a pesky, but clever, scientist, the author winds up taking on the role and identity of his fictional creation. And apparently, the author, who was pretty much a drunk and a jerk, finds that the selflessness and heroism are less and less of an act as time goes on.
Will Traveler in Traveler becomes fond of the two roommates he's setting up, and ends up sparing their lives (at great cost to him later), against the plans of his employers.
Cole Turner (Belthazor) in Charmed was sent to kill the Charmed Ones before love redeemed him and he abandoned his demonic power. Subverted in that he eventually found himself in dire need of power to protect his loved ones and snapped back to his demonic conditioning and tried to marry Phoebe in part of a long plot to set her up as queen of Hell and effectively spawn The Antichrist.
In Highlander, Kronos tells Methos that he's been pretending to be reformed for so long that he's started to believe it himself. When MacLeod learns about Methos' past, the resulting argument causes Methos to go back to Kronos.
Faith began her Heel-Face Turn like this. She switched bodies with Buffy. But after living only one day as Buffy, she effectively became Buffy. Or rather, her own semi-warped sense of what Buffy was like. She even attacked Buffy-in-Faith's-Body, screaming that she was evil.
The latter was most likely a reflection of her own pre-existing self-hatred rather than a result of becoming the mask.
Also, she deliberately practiced what she believed to be Buffy's catchphrase, "Because it's wrong," in order to deceive Buffy's friends (and Spike), but ends up using that exact phrase when facing a group of vampires in a church. That one time, she actually means it too.
Another Buffy example: Jenny Calendar is revealed to be Janna, a member of the clan of gypsies who cursed Angel with his soul, after he experiences 'true happiness' with Buffy and reverts to the evil Angelus. It's heavily implied that her love for Giles ("I didn't know I would fall in love with you") led to her Becoming The Mask, and after she is killed by Angelus, she's buried under her assumed name of Jenny Calendar.
Glory has taken on more and more human traits over the years, much to her annoyance.
An unusual example of this takes place in The Sarah Connor Chronicles episode "Allison from Palmdale." Cameron, suffering a glitch due to damage to her chip, briefly adopts the personality of Allison Young, the resistance fighter whom she was modeled after and whose personality she copied, before going off to assassinate John Connor.
A somewhat perverse version occurs in Dexter, where Dexter begins as a completely amoral psychopath who's also phenomenal at pretending to be normal — but after a while, pretending to be normal starts to get to him... Unusually for the trope he seems to find Becoming the Mask an improvement on being a type B Stepford Smiler and welcomes it. He even advises a budding Serial Killer to do this in an attempt to stop feeling empty.
In Kamen Rider Kabuto, the Scorpioworm assumed the identity of Kamishiro Tsurugi, but prior to the beginning of the series somehow came to believe himself to be Tsurugi to the point at which even he is shocked when the mask slips.
Played out interestingly in Prison Break: T-Bag (who is someone who definitely can't redeem himself, despite being awesome) has this with his fake identity of Cole Pfeiffer, a charming top-salesman. He actually hopes to leave his past as a convict behind, because he really seems to love his role. In the end, it doesn't work.
T-Bag: "You realize what I'm giving up here? I was guaranteed 50 grand!"
Gretchen: "You're crying over 50 grand, are you serious?!"
T-Bag: "I have a job! I make money, I get mail, people call me sir." Gretchen: "12-hour days and eating left-over lo-mein. Something tells me Theodore Bagwell wouldn't last long in this situation." T-Bag: "Yeah, maybe. But Cole Pfeiffer would."
Subverted in a later episode: T-Bag takes a proactive step towards being a Cole Pfeiffer-kind of guy by not killing a man he's holding hostage, who could be either an innocent Bible salesman or an evil Company agent. Turns out he was a Company agent after all. Violence ensues.
In the original UK version of Life On Mars, Frank Morgan suggests this as the cause of Sam Tyler's condition. The series also ends on this trope with Sam willingly immersing himself into 1973, though exactly how he does this is never fully revealed.
In season four of NCIS, Tony begins a year-long relationship with Jeanne Benoit as part of an undercover operation against her father, arms dealer La Grenouille. He genuinely falls in love with her in the process, which doesn't stop him from answering her inevitable "Was any of it real?" with a simple "No."
The same idea was used in an episode about North Korean sleeper agents, in which one of their number turned against the rest for the sake of her American husband and baby daughter.
Ziva also turns out to be someone who was originally sent as a spy, but grows more loyal to NCIS than her father and Mossad; so much so that she became a naturalized US Citizen so she could stay on as an official NCIS agent.
A bittersweet version occurred on a Mother's Day episode of Saturday Night Live: The late Phil Hartman is with his mother, and he cannot get out of character. His mother calls him on it, and he realizes that he's spent so much time as other people he doesn't really know who he is. Mom knows who he is, though, so it'll be okay. sniff
That also happened in Hartman's monologue when he first came back to host in season 21, where Hartman does his monologue in different voices and runs crying into his dressing room, realizing that he's been playing so many characters and doing so many celebrity impersonations that he doesn't know who he is anymore.
Similarly, when he appeared on The Muppet Show, Peter Sellers informed Kermit that he had had his real self surgically removed. (See his entry under Real Life, below.)
In My Name Is Earl, Earl at first only tried to make up for all his past bad deeds because he believed "karma" would punish him otherwise. But eventually, he starts to really care about people.
Same with Billie, who at first hides among the Camdenites (radical Amish) while plotting revenge against Earl. However, the simple lifestyle eventually wins her over, and she joins their community, giving Earl all her money.
This happened to Glenn too, though in the opposite direction. He was a good-natured boy scout until he was thrown in juvie for something that was Earl's fault. He had to pretend to be a badass to survive in there, but he eventually internalized it. By the time Earl met him again, he was such a psychopathic criminal that everyone else in prison was afraid of him.
The Twilight Zone episode "The Masks" does this, quite naturally, with a Karmic Twist Ending: a dying man makes his overly-eager-for-the-inheritance relatives wear masks as a condition of inheriting. The masks are nasty caricatures of their inner selves, and they end up quite literally Becoming the Mask.
Oz. Undercover cop Desmond Mobay, posing as a Jamaican drug dealer, gets hooked on drugs and murders a corrupt cop turned inmate who threatens to blow his cover. Another prisoner, convicted copkiller Augustus Hill, realises who Mobay is and calls him out over his hypocrisy. Mobay beats Hill unconscious, but then confesses to the murder, realising he's become one of the criminals he's supposed to be fighting.
Jazz Hoyt turns out to have been a Harvard law student who went insane and started believing himself to be a biker, which led to him actually becoming one. This meant that technically he was no longer delusional; this and the administrators' lack of interest in his past made them oblivious to any of this for a long time.
Shillinger arranges for Chris Keller to be Tobias's new roommate when he's introduced as part of a long ploy to ingratiate him to Tobias and eventually betray him, causing sincere emotional distress. This ultimately backfires when the new roommates fall in love and proceed to cause Shillinger grief for the remainder of the series in a cycle of revenge plots.
The X-Files: An alien invader, infiltrated as a human baseball player, eventually decided he was a better person that way. When another alien came to execute him and ordered him to show his real face, he answered that it ''was'' his real face.. Even his poisonous blood has somehow changed human when he is killed.
Even Scully sort of qualifies as this. The original reason for her assignment to the X Files was to spy on Mulder and discredit his work. Though in her case, the powers that be chose the wrong person for the job, since it didn't take her long to become close friends with Mulder, join him on his crusade and even eventually help expose the man who gave her the assignment in the first place, Section Chief Blevins.
When Chuck Bartowski first became the Intersect, it was an accident, and he was forced to work as a spy and foil terrorists and other bad guys against his will; a fact he complains about constantly. The show focuses on how Chuck slowly but surely begins embracing his saving the world role without coercion. Agent Walker in particular points out that although he denies, he really is a hero. At the end of Season 2, Chuck literally becomes the Intersect, again. And this time completely by choice.
Sarah also finds herself actually falling in love with the guy she was supposed to be fake-dating for the sake of their covers.
A flashback scene even shows that Sarah initially considered Chuck a dateless chump and that seducing him would be a "piece of cake."
An interesting case with a nerdy British young man who became a test subject of an experiment similar to the Intersect project, except this one involves completely replacing the subject's personality with a new one in order to create a perfect mole. Unfortunately, it ends up working a little too well. The man becomes one of the most powerful criminals in the world, being none other than Alexei Volkoff, a Magnificent Bastard.
Although he never forsook his real loyalties, undercover fed Vincent Terranova often formed strong personal connections with the criminals he investigated on Wiseguy. His friendship with Sonny Steelgrave was so genuine, Vinny openly admitted he would have allowed the mob boss to escape, had Sonny not personally beaten a man to death in front of a hidden camera.
Doctor Who — Being stranded on Earth, Blon Fel-Fotch Passameer-Day Slitheen got to know and enjoyed the everyday human rituals she conducted as Margaret Blaine. To the point where the Doctor has to point out that she is pleading for mercy from a dead woman's lips.
Blon also shows signs of getting too into the part earlier when her escape plan causing destruction on a global scale is discovered by The Doctor & Co. When queried why no human authorities had noticed a nuclear power plant in the middle of the city designed to go apocalyptic?
Blon: London doesn't care — the South Wales coast could fall into the sea and they wouldn't notice? Oh? I sound like a Welshman. God help me, I've gone native!
The Doctor himself states that his "real" name doesn't matter in "The Name of the Doctor", stating that your name is a promise you make.
In the Hartnell-era story "The Aztecs", Barbara has been mistaken by the Aztecs as a godlike reincarnated priest and assumes God Guise to play along, in the hope of influencing the culture into abolishing human sacrifice. The Doctor rants at her in a notorious scene - "You cannot change history, Barbara, not one line!" to which Barbara replies, "Not Barbara; Yetaxa". She even refers to herself with the Royal "We" from then on.
In Mr. Monk Joins a Cult, Monk joins a cult to investigate claims that its leader murdered an ex-member, but he actually starts to get sucked in to its teachings when he finds that they help him overcome his OCD. It's also present to a lesser extent in the episodes where he goes undercover as an office worker and a butler, only to find that those jobs suit someone with his obsessions extremely well.
On the other hand, pretending to be a hitman who happens to look identical doesn't work out so well.
And in Mr. Monk and the Actor, an actor playing Monk in a movie based on an earlier Monk case (Mr. Monk and the Astronaut), the actor gets so wrapped up in the part that he believes he's the real Adrian Monk.
Angel: Lilah admits to Angel in season 3 that she became her "game face" long ago.
Happens to Quinn in Glee - she first joins the club to spy on it for Sue, hoping Finn would lose interest in Rachel if the club disbanded. She ends up enjoying the club enough that she does a complete Heel-Face Turn, even saving the club when Sue seems successful in disbanding it. (It's debatable, though, how much Quinn would have Become The Mask if her pregnancy hadn't turned her into a Fallen Princess, though.)
Also Santana who was also a spy at first but has admitted that Glee club is the best part of her day.
Quinn's case is a lot more complicated than a simple straight playing of the trope. For one, it could be argued (and the show gives glimpses of this) that her previous identity as Alpha Bitch and Seemingly Wholesome '50s Girl was more of an act than her role in the Glee Club, but she didn't realize it until she got pregnant and Glee was the only thing remaining from her former life. Certain scenes suggest that Quinn was under a lot of pressure from both Sue and her parents to live up to certain expectations, whereas Glee gives her more of a chance to truly express herself. So it may be more of a Secret Identity Identity - maybe we don't always know which part is "real" and which is the mask.
Leverage has a humorous non-evil version. Eliot has to play the part of a baseball player as part of a con, but as he tells Hardison before the con, he doesn't like baseball. However, as the con goes on, it turns out that not only is Eliot really good at baseball, but he starts to enjoy it too. He even gets a sandwich named after him. It leads to the following exchange:
Nate: All right, good news, bad news.
Tara: Good news?
Nate: The mayor's hooked. We're in the pinch.
Tara: Bad news?
Nate: I think we lost Eliot until the playoffs.
This was also the in-show reason for Sophie's absence when Gina Bellman went on maternity leave. Sophie had worked under so many different personas as a grifter that she wasn't sure who she was anymore, and she needed time to really find herself. Sophie isn't even her real name, it is merely the name she had adopted as her primary identity.
In Season 2 of Alias, Allison Georgia Doren, disguised as a replica of Francie Calfo, actually falls in love with Will Tippin and is visibly upset when she is forced to kill him.
In a Season 2 episode the wife of an American mathematician (guest star Christian Slater) turns out to be a Russian agent who fell in love with him for real. It also turns out her husband was an NSA agent and knew his wife was all along.
In one episode of Xena: Warrior Princess some random guy shows up wanting to kill Xena to build his reputation as a warrior because he wants to become a great warlord. He claims to have killed other fearsome warriors as well. While he does have the skill to back up his claims, it turns out he has never killed anyone in his life — Xena realized this when she remembers that she actually killed one of the warriors he mentioned. Xena warns him that people eventually truly become what they pretend to be after a while. At the end of the episode, the guy decides to pretend to be something he can live with and try his hand at being a hero.
Fringe: One shapeshifter at least (maybe two) got very attached to their family.
Another example occurs with Fauxlivia, who impersonates the real Olivia in order to gain Peter's trust and eventually begins to develop genuine feelings for him.
A similar thing happens in the Supernatural episode All Dogs Go To Heaven. A skinwalker disguises himself as a family dog, waiting for the call to attack and turn the family. He eventually grows to love the family, and almost dies to defend them.
In an episode of White Collar, "Forging Bonds", it's shown that Neal went with the alias Nick Halden to work for Vincent Adler. As Nick Halden he meets Kate, and he has a good life going for him, to the point where Mozzie has to keep reminding him about the con he's trying to run. He even blows off the con for Kate at the con's most pivotal moment. He only came clean when Adler conned him out of every penny he had, and that was only because the old life was the only one he had left and he wanted Kate to stay with him.
Another episode has Peter going undercover to the point that he starts to really enjoy his fake job.
Detective Inspector Zain Nadir of The Bill is warned of how this can occur to undercover detectives who stay in a role for too long. This somewhat happens to him too when he becomes romantically involved with a drug dealer.
In the New Tricks episode "Only The Brave" it turns out the murderer was Reverse Mole, Knowles, who had gone native in the gang he was sent in to investigate.
Breaking Bad: Walt creates the persona Heisenberg when dealing with the criminal underworld. As he gains more and more power, the ruthless, murderous Heisenberg becomes his new personality, and the mild-mannered pushover that was Walter White becomes the mask, to no longer existing by the time season 5 rolls around.
Jesse has two of his junkie friends infiltrate his 12-step program to sell meth to the other addicts. They don't have much success. Later Jesse learns that his dealers are actually doing the steps for real and taking pride in their recovery.
This is what happens to Horatio's brother Ray in CSI: Miami, while he's undercover in South America. He ends up going dirty and gets killed because of it.
Person of Interest: "John Reese" is just a cover identity he was given when he became a government assassin. He discarded his life before that and became the new identity.
An episode of Human Target has a man find out that his wife is a deep-cover Russian spy. When Chance exposes her, he finds out that she had gotten married as part of her cover but has actually fallen in love with the guy since then. Unfortunately, her old contacts have come back expecting her to do her job. She non-fatally shoots her husband in front of her accomplices, and Chance (who figured it out) then non-fatally shoots her in front of them. The couple then get new identities, and can live without being pursued by her former partners.
Elementary: Moriarty seduces Sherlock into a relationship in order to get close enough to him to study him. She didn't count on actually falling in love with him. This proves her undoing when Watson correctly deduces that it has happened.
Pennsatucky on Orange Is The New Black. Prior to her trial, she was a meth-head getting her fifth abortion. When she killed a nurse at an abortion clinic for "disrespecting her", pro-life activists assume she was one of their own and raised money to get her a good lawyer. Pennsatucky played along but eventually became a hardcore, pro-life, right-wing Christian.
And if our kindness This day is just pretending If we pretend long enough Never giving up It just might be who we are
Melanie Safka's "The Good Guys" is all about this.
You're going to play the good guys By singing the good guys' hymn — You're building the halls with the outer walls But you haven't got a thing within... Eventually, the whole facade Becomes more than a whim. By starting to build on the outside You're gonna fill up the walls within.
In the most literal sense possible in Styx's "Domo Arigato Mister Roboto" music video
The time has come at last To throw away this mask So everyone can see My true identity... I'm Kilroy! Kilroy! Kilroy! Kilroy! (He says as he removes his mask, but rather than a human face like before, he's become Mr Roboto)
Myth and folklore
One medieval legend is a very literal taking of the trope, that of an ugly man who for years wore a mask that made him beautiful until when he finally took it off, he found that his face had grown into the mask's shape, making him truly handsome.
At least one variant of this story has an old enemy from before he began wearing the mask slip into a party the masked man is throwing and steal his mask, hoping to ruin his enemy. Instead the above realization occurs.
Chris Jericho originally set out with Christian to con Trish Stratus and Lita, respectively, into sleeping with them by being lovey, helpful heroes. Along the way, though, Jericho actually developed feelings for Trish and regretted the con, trying to talk his way out of it when the women found out. Trish was already feeling betrayed and well underway with a Face-Heel Turn by the time he got around to it, though.
The Craftworld Eldar of Warhammer 40,000 once created a Chaos God from their excesses, and so the survivors follow a life of strict discipline called the Path. Each Eldar focuses on one role at a time - poet, artisan, warrior, seer, etc. - and cultivates a new personality based on that vocation, which can be set aside and returned to later. In the Aspect Warriors' case, part of their training is the construction of a figurative "war mask" allowing them to fully embrace their violent tendencies when needed and avoid being consumed by them, which must be mastered before the warrior is allowed to don the actual war mask of their armor. Despite such precautions, some Eldar become trapped on their current path, so that seers become Farseers obsessed with reading and altering the future, or a warrior becomes an Exarch who lives only to battle and train others for war, forgetting their past life and taking the name of the first to wear their armor.
The Dungeons & Dragons setting Eberron has this as the basis for one of the Changeling philosophies. Natural shapeshifters, Changelings of the Passer philosophy do their best to forsake their true nature, creating an identity of another race and adopting that as their 'true being'. While they can still shapeshift, they are very uncomfortable doing so, or even reverting back into their real form, as their 'mask' becomes their true identity. The other two philosophies are similar; Seekers aim to embrace the 'ultimate form', which they believe to be an extension of the Changeling's true form, while Becomers are similar to Passers, but assume myriad different lives and identities, all equally real to the Changeling.
This is likewise what happens when a demon Falls. They've lived a cover story in order to fulfill the will of the God-Machine, perhaps one that had a profession, friends, even a family. But they only view such things intellectually, without any true connection. Once a demon Falls, the emotional context comes flooding in, and while there may still be some disconnect, all the elements of her Cover mean something.
Personamancers in Unknown Armies base all their magic around pretending to be other people (or screwing with other peoples's self-identification). They charge their magic through pretending to be other people. Here's the catch: to gain the power for such an act, they have to really believe they're somebody else, at least a little. And gaining recognition as themselves kills their power. One of the quickest ways to gain power is to pretend to be somebody else into a mirror for one hour. Do that every day for years and eventually, you start to buy it...
This has been the fate of more than one Scorpion spy in Legend of the Five Rings. In fact the sourcebook "Secrets of the Scorpion" notes that the spymaster who trains these men sometimes cries quietly in the night after having portrayed a brave and noble hero, beloved by many. He assumed the role by murdering said hero and living their life for five years, during which he performed true feats of heroism to maintain the cover. He has never impersonated anyone ever since.
In BattleTech, the Wolf's Dragoons mercenary unit was originally a scout unit from Clan Wolf sent to spy on the Inner Sphere. When the main Clan force invaded, however, the Dragoons changed sides and fought for the Successor States.
Bertolt Brecht's Man Equals Man is made of this trope. The plot centers on harmless everyman Galy Gay, who runs into a group of British soldiers on the way home from the market. Because they don't want to be punished for losing group member Jeraiah Jip while out drinking, they ask Galy Gay to take his place for roll call. When that's done, the group leader decides to completely change Gay's personality just for the lulz. One fake elephant, staged funeral, and castration later, the new Galy Gay/Jeraiah Jip is enthusiastically leading a savage attack on rebel forces in Tibet. (In the meantime, the old Jeraiah has assumed the place of an oracle at the temple where he woke up hung over.)
Charlie Baker from The Foreigner. By the end of the play, Charlie has become the Foreigner to the point that he remains in character around Froggy, the one character who knows he really speaks English.
In Martin Guerre, Arnaud du Thil is initially reluctant to assume the identity of his friend Martin, but as the musical progresses he grows to love Martin's village, life, and especially his wife Bertrande. By the time he is put on trial for 16th century identity theft, he seems to really consider himself 'Martin Guerre' and even sings a reprise of Martin's song, 'I'm Martin Guerre.'
Zachary Comstock of Bioshock Infinite is a complicated case, mixed over with Believing Their Own Lies. He works tirelessly to keep up his image as a religious leader, lest he be forced to face by the guilt of his truly horrible past, and has spent so much time abusing his knowledge of the future that he truly believes himself to be a prophet. He boasts about Wounded Knee, even though the atrocities he committed there were what drove him to abandon his past identity as Booker DeWitt and become Comstock, and he would declare anyone who suggested this a traitor. A Voxophone found in the Clash in the Clouds DLC has Rosalind say this of him explicitly.
When he comes to Rapture and becomes Booker once more to escape the guilt of Elizabeth's death in Burial at Sea, he loses all traces of his "Comstock" persona, so that the ending once more comes as a shock.
In Tales of Legendia, Senel infiltrates the village where Shirley and Stella live, acting as a soldier of Vaclav. Senel pulls a Heel-Face Turn while there and forgets about his mission, wanting to live in peace beside them. But, that doesn't last.
Cait Sith in Final Fantasy VII, who joins the party as a spy and then grows to care about them and joins them for real.
Only superficially fits as an example. Reeve was already sympathetic to most of the party's issues, but sincerely did not trust Avalanche. He didn't so much change personality wise, but realize that Avalanche was operating on the same wavelength he was.
Leliana from Dragon Age. She was originally basically an assassin, and she had to flee her home country and go undercover. She pretended to be a sweet, bubbly girl with a strong faith in the Maker—then she decided she actually liked the whole "being happy" thing.
Morrigan also has some elements of this, pretending to like the male player character in order to get into bed with him and then actually falling in love.
The whole plot of Super Robot Wars Advance pretty much revolves around this, depending on who the protagonist is. If it's Axel Almer, he got amnesia after doing the dimension jump to infiltrate the protagonist group and had enough time to befriend them and leave a good impression, and when it came to his time to return, he realized that his group was wrong and elected to stay on the new group, fighting his previous superior. Same thing happened to Lamia Loveless, except that she got no amnesia, but her orders usually come too late, and she already blended with the society, making her realize she has a conscience and values it, thus making her reject the fact that she's a mindless doll and betray her superiors. And the protagonist's reaction to them? Forgiving as ever.
Ditto Decoy Octopus in Metal Gear Solid: According to his bio, he has to undergo psychic therapy after he's done being disguised as someone else, since his disguises are absolutely perfect down to the slightest detail... including blood type and DNA.
The guy even files down his cheekbones where necessary to ensure that the shape of his face is the same as his disguise's.
And later in Metal Gear Solid 4: Guns of the Patriots, we have Revolver Ocelot, who specifically tricked himself into thinking that he was Liquid by way of hypnotherapy and (what else) nanomachines, so that he could fool the System and gain access to the Patriots' AI.
Metal Gear Solid: Peace Walker: Paz/Pacifica Ocean, a Double Agent for Cipher, a.k.a. Zero and the Patriots. Her diaries reveal that she goes from outright despising and deriding Big Boss and the members of his army to wishing she could spend a few more days with them before carrying out her orders.
In The Force Unleashed, Starkiller spends time gathering "allies" while pretending to be a Jedi. Over time he begins to make good decisions, and begins to play the part very convincingly. By the time Darth Vader betrays him, he realizes that he IS a Jedi. And goes on to challenge the Sith. He saves the rebels, but it doesn't go well for him.
Rival Schools pulls this off in both series' games. Kyosuke Kagami's work with Taiyo High in United By Fate convinces him that his twin Hyo's plan may not be the best idea, while Yurika Kirishima's time at Seijyun High (and specifically inspired by her best friend, Akira) in Project Justice moves her to betray her younger brother Kurow.
Iris in Phoenix Wright Ace Attorney: Trials And Tribulationspulled a Twin Switch with her Evil Twin sister Dahlia to keep her from killing her boyfriend Phoenix, but she came to truly like the guy and couldn't even take the item she was supposed to get from him to keep her sister from killing him.
Then in the final case of Dual Destinies, we have the phantom, an assassin who has become so many masks that he's completely forgotten his original identity.
Inverted in City of Heroes when one story arc has you tracking down an undercover police officer who turns out to have fully joined the villain group he was infiltrating.
This is possible for the player if you choose to start in Praetoria. You're required to choose a philosophy (Loyalist or Resistance) at the start of the game. Players can choose to do missions for the opposite faction, periodically contacting their faction leader to twist the results one way or the other. As long as you continue to periodically contact your faction leader, you're still considered to be "undercover". However, it's incredibly easy to find yourself "forgetting" to check in with your former faction leader...
Vanessa DeVore, leader of the Carnival of Shadows, coincidentally managed to find and put on an actual mask containing the soul of one of her ancestors. At first the two struggled for control of her body, but eventually began to work together, making Vanessa (formerly a normal, non-evil person) a violently hedonistic villain with Psychic Powers.
In Prototype, Alex Mercer is quite explicitly dead and gone. However, the corpse was subsumed and reanimated by the Blacklight virus, which imitated him so completely, so perfectly, that The Virus believes it is Alex Mercer. Even after it finds out the Awful Truth, "Mercer" is changed by the experience, evolving from monster that Mercer was as a human, to a rampaging sociopath with occasional flashes of heroism, to a Sociopathic Hero, given that he protects New York from being nuked when it would have been far easier for him to simply do nothing and save himself.
Also happens a lot in Mitadake High when the Killer/Kira starts befriending others in order to betray them later, and ends up caring about them, and even sparing them at the end of the game. A weirder version can happen when the killer/kira doesn't notice that they are the killer/kira and plays the entire game as if they were innocent.
Discussed in The Legend of Zelda: Majora's Mask. One of the children that you play hide 'n seek with at the end of the game questions that, "if you have so many masks, what is your real face?"
"Your true face... What kind of...face is it? I wonder... The face under the mask... Is that...your true face?"
Taichi in Cross Channel is literally in the 'becoming' part of this trope. He's really trying hard not to be completely insane and connect with people, unlike Youko. The mask slips every now and then, causing all of his relationships to be extremely unstable. The best example of this would probably be the small slipup that occurs right after Yutaka committed suicide and he ruins his relationship with Kiri. She thinks he killed Yutaka, when in truth he didn't really care much anymore. Before and after that, she's probably the only person apart from Youko who truly understands him fully.
Kessler in inFAMOUS is unrecognizable as Cole's future self; he keeps a memento to remember his previous life by, but after fifty-plus years of scheming and plotting and acting how someone has to act to reach his position and maintain it, he's not that person anymore.
Ninja Maid Cecilia of Vanguard Bandits initially hates the whole maid idea. But by the end of the game she's grown to love it so much she gets into an argument about wanting to keep all her maid costumes.
Margarete in Shadow Hearts talks about this in one scene. She was ordered by the "Powers" (presumably, the French, whom she worked for) to spy on the crisis in Asia, where the game starts. When she meets Yuri, she fully intends to use him to benefit her nation. However, as she worked with him, she grew attracted to his comic book-esque ways. She never follows through with her mission.
In Skyrim a wizard sets up a Scooby-Doo Hoax, masquerading as the guardian spirit of a Nordic burial ground to keep superstitious locals from discovering that he's attempting to loot the tomb. After six month of failing to solve a puzzle-locked door, he goes insane and becomes convinced he's an actual guardian spirit.
Magical Diary has Damien nearly done with the con he's been pulling on you all year (and on the school in general for the past four years), only to find out that he can't finish what he started. The realization causes him a few problems.
Sleeping Dogs's Wei Shen is described in his San Francisco police psych profile (before an undercover assignment for SFPD) as having "chameleon-like tendencies" which make him so "highly adaptable" that his handler needs to ensure that Wei doesn't actually change sides; by the end he's less an undercover cop than a triad gang leader who's quietly cooperating with the police on a few cases.
Kisuke, of Muramasa The Demon Blade infiltrated the household of Torahime as a servant to discover and steal an ancient demon blade her family was charged with protecting. During this time he fell in love with Torahime, and so, when the time came for the rest of his ninja clan to come and steal the blade he fought on the side of Torahime against his old companions. He fails, gets amnesia and spends much of his story trying to atone for his actions.
Suikoden V gives us Euram Barows, who, at first glance and throughout the game, shows us to be a foppish, idiotic buffoon. Background information received from Oboro, and information learned after his Heel-Face Turn, shows that he actually starting acting this way to comfort his mother, who was mad with grief over the death of Euram's older brother Hiram, assassinated during a civil war prior to the game. Between that, the influence of his father, and Euram's own emotional weakness, this act became real. The real Euram is a demure guy who blames himself for a lot of problems.
Trish from Devil May Cry is posing as Dante's guide to Mallet Island in order to kill him for her master, Mundus. By the time she reveals her true colors in mission 20, Dante is so mad at her for this and leaves her behind. This gives Trish to stick her role as his guide for real.
Happens in Ever17 with Kaburaki "The Kid" Ryougo impersonating Kuranari Takeshi in Kid's (Hokuto's) routes. It's done so well that half of the plot hinges on it, but Kaburaki gets a little bit too intimate with his fake personality. A given, since he's been practicing non-stop since 2017.
Between Tsukihime and Melty Blood, Meido Kohaku goes from sinister Chessmaster with no emotions who is planning the downfall of the Tohno family through drugging them; to really being the lovable goofball she pretends to be; who possibly makes robots and rides around on a broom in her spare time.
Note, however, that the robots and broom-riding may have been influenced by Tatari, and she's STILL trying to play everyone like saps. She's just more...nice...about it.
In Hisui's route it's revealed that she was becoming the mask, she just followed through on her plan anyway because she had no idea what else to do. In her own route, the mask starts to crack when Shiki pays attention to her and she reveals she honestly has no idea how she really feels anymore, so she leaves for a little while and becomes/reverts back to a very sweet, kind person.
An interesting example occurs with Anevka in Girl Genius. After being damaged in an experiment as a young girl, her body is stuck in a nutrient tank and attached to a Clank that allows her to interact with the outside world. At least, until her brother reveals she died years ago; the Clank ended up developing its own personality and came to believe it was Anevka. In other words, the mask became her.
The "bad" version happened in the backstory of Juvenile Diversion: Courtney "infiltrated" the cheerleaders to get revenge on them, then promptly became just as much of a bitch as them.
There's an interesting mental disorder in Mary Sue Academy called Character Shock Syndrome Sue. It's where a Mary Sue become the character they portray. Jessica Pluto suffers this.
Kevin & Kell has a pretty mild example when Fiona chose to disguise herself as her boyfriend Rudy to avoid paparazzi. Unfortunately, she started to act like Rudy as well: moody, lazy, irresponsible. Rudy had to literally knock the disguise off her by acting responsible. Fiona later vowed to avoid this trope so much by choosing to disguise herself as someone with as much work ethic as herself. (Since she chose Lindesfarne, it works...but she starts craving bugs.)
A shorter example was one strip where a group of predators fell into the rabbit warren, forcing them to disguise themselves as rabbits until they find a way out. At least one of them ended up spending the rest of his life there, growing old and marrying and still wearing that rabbit disguise.
In Sticky Dilly Buns, Ruby disguises herself as the rather "sketchy" guy "Rudy" while helping Dillon with a Zany Scheme. It soon seems to do her confidence some good, and she specifically claims that "Rudy" is rubbing off on her. Even if this it serves as an excuse for her snarking at Dillon, she perhaps manages more and sharper snarking than usual — and then she uses that confidence to save a distressed Dillon from an annoying guy, at a little personal risk and despite the fact that she doesn't especially like Dillon.
In Survival of the Fittest version three this happened to Dominica Shapiro, who initially joined the group SADD on the off chance their plan would work, with the intent on a double cross if not, but gradually became more and more part of the group properly.
In Plague and Treachery on the Oregon Trail, it's revealed that Susan was a British spy sent to overthrow America from the inside, but she eventually came to love the family she created as a cover, and abandoned her assignment.
Wannabe Heroine Taylor, the protagonist of Worm starts off joining the Undersiders due to a combination of looking evil and the heroesneedinginformation on them. Over time her disillusionment with the heroes and the friendship she finds among her team complicates things, and she decides to stay with them. Interesting in that it's a hero to villain example, although most of the superheroes and supervillains have Greyand Grey Morality.
While everybody in Suburban Knights is trying to stay in-character, several of them do so with more...commitment than others. Obscurus Lupa claims that she should be useless in battle because of her character choice, Paw Dugan tries to gather rage from everybody (including the trees), and Phelous seems to have gone right off the deep end. MarzGurl also seems to be joining the throng, what with speaking only in Japanese, scenting the air and biting the Critic on various portions of his anatomy.
In the end, Phelous reveals he was just acting and Lupa said 'fuck it' and joined Angry Joe in shooting things with a machine gun
Played for Drama with The Nostalgia Critic's entire running time. First intended to be a Cartman-like figure, he moved away from that quickly and started doing good things because he was desperate for people to love him. In Suburban Knights, he started to selflessly care for people and by To Boldly Flee and beyond, he's a true hero who takes every opportunity he can to care for his universe.
A fair amount of the My Little Pony: Friendship Is Magic fanbase started out as Internet trolls who started pretending to be obsessive fans of the show just to get other people confused and/or irritated. It's My Little Pony, what teenage boy or man could possibly enjoy such a series? Well, as the trolling went on, the majority of them started to find all the little Parental Bonuses and Shout Outs, and of course, Lauren Faust's contributions to the show, making it fun to watch even for the parents of the target demographic (girls aged 5-10). The trolls started legitimately liking the show. Some even stopped their pony-themed trolling out of respect.
Dramatic Detective of LIS_DEAD admits in the comments of an early post that he identifies himself more closely with some of his aliases than the name his own mother gave him.
When she got turned into Vriska in We Are Our Avatars, Nichole has attempted several times to convince people she's the actual Vriska for fun, and as a result has gained a lot of Vriska's habits such as the speech quirks and the obsession with levels. However, she's astonishingly terrified of becoming a "8luh8luhHuge 8itch" like Vriska, and is constantly asking people to keep her in check to prevent her from going off the deep end.
Shayera Hol aka Hawkgirl of the animated Justice League joined the team as an alien spy, but then decided to help them form a counter-offensive, when she found out what her race was really planning to use the Earth as a hyperspace bypass in an interplanetary war, which would destroy it. Feeling guilty of betraying both the Justice League, and her homeworld of Thanagar, she decided to leave the team before they announced their decision on whether she can return.
Terra (in the Animated Adaptation only) of Teen Titans really began to feel at home with the team and fell in love with Beast Boy. She tried to compromise by saving him and letting Slade kill the others, and, well, you can guess how it turned out.
Done dramatically in the Batman: The Animated Series episode "His Silicon Soul". An android duplicate of Batman created by the mad computer HARDAC is trying to complete its mission, breaking into the Bat-Cave to hijack control of the computers and resume HARDAC's mission, replacing all of humanity with robotic duplicates. But it seems that HARDAC duplicated Batman's personality only too well, and it starts to develop the true Batman's sense of morals, struggling between right and wrong and whether to do as its programming commands or reject what it knows is evil. Eventually, after a fight with the real Batman where the android thinks that it has killed him, it is overcome with grief over what it has done, and destroys the computer, destroying HARDAC's program and itself in the process, ending HARDAC's threat forever. In the final scene, Alfred and Batman - who survived, naturally - inspect the androids remains, and Batman ponders if it might have had a soul. "A soul of silicon," muses the Dark Knight, "but a soul nonetheless..."
The assassin droid Zeta in Batman Beyond replaced an accountant, as he was investigating money laundering by a terrorist organization. Once he completed the mission he ended up running into the guy he was impersonating. Per protocol, he should have eliminated the man on the spot. The aforementioned time spent with the man's family affected him to the point that he could not bring himself to deprive him of that experience, and so went rogue instead (leading into his Spin-Off series, The Zeta Project).
The Legion of Super Heroes cartoon has evil shapeshifter Ron-Kar finding himself sympathizing for real with the good guys, and even willingly helping them, after his Memory Gambit infiltration is exposed.
The Looney Tunes cartoon Bugs' Bonnets (1956) plays with this idea by casting it in the form of people taking on roles defined by the hats they wear — and then throwing Bugs Bunny and Elmer Fudd into a landscape littered with hats scattered from a passing truck. How many times — and to what degree — can these two Become The Hat? Needless to say, it gets typically extreme.
Taken to ludicrous extremes by Roger in American Dad!. He creates a new identity to seduce a shop girl and allow him to steal a pair of gloves he likes. Then the stress of actually caring about someone causes Roger's mind to split into two - the persona he created, and himself. Apparently his persona carries on for quite a while before Roger notices extra bills on his credit card, at which point Roger tries to destroy this man's life.
Not to mention the little roleplaying activity that he and Francine improvised for themselves...
An episode of Fillmore! has Ingrid going undercover in a close-knit mafia-esque Girl Scout Troop. She genuinely befriends the group, making it especially hard to go through the sting. As an added bonus, their leader was the Safety Patrol's previous undercover agent gone rogue who was much more loved and popular than Ingrid, which made them believe Ingrid could be more susceptible to this op.
Seymour Skinner in The Simpsons. In the episode "The Principal and the Pauper", it's revealed that he is actually Armin Tamzarian. He served with the real Seymour Skinner in Vietnam and took over Skinner's identity when he was apparently killed. Twenty years later, the real Skinner shows up in Springfield to reclaim his identity. But the townspeople decide they prefer to keep the Skinner they're used to. The real Skinner is banished from town, Tamzarian is put back in Skinner's identity, and it's ordered that nobody will ever mention this incident again.
Cartman fakes having Hollywood Tourette's in order to have fun with his usual language habits, only garnering sympathy rather than derision from authority figures. He forms a plot involving this to say antisemitic things on Dateline, but by that point he unconsciously began blurting out personal secrets such as "I'm making all of this up!", "My cousin and I touched each other's wieners!" and "I wet the bed!"
In "Butters' Bottom Bitch", Officer Yates assigns an undercover agent for a series of prostitution busts: himself. During the operations, he makes his arrests after performing the sex act, each one becoming more and more elaborate, to the point of gangbanging a college fraternity. He even marries the Big Bad pimp at the end of the episode, living with him for months before finally deciding to place him under arrest.
Brock Samson of The Venture Bros. He was originally assigned to prevent Rusty Venture from ever activating the ORB and was put under the guise of the Venture family's bodyguard, but after several years of protecting them he truly began to feel like part of their family, and even purposefully refused to kill Rusty when he discovered the ORB.
It's heavily implied that until that episode, Brock didn't know what his real mission was.
Also his predecessor that protected Venture's ancestor. He broke/damaged the ORB to the point it would never work instead of killing him. Leading to the events of the episode.
Discussed in the Daria TV movie "Is It Fall Yet?," when Daria's mom forces her to work as a counselor at a day-camp for children.
Daria: And I judge myself unfit for human contact.
Helen: That's exactly what you will be if you don't start engaging with the rest of us! You keep hiding your real face behind that antisocial mask and one day the mask will be your face. I'm not letting that happen. You're working at that camp! (leaves)
In one of the old Tom and Jerry episodes, a duckling comes to think of Tom as his mother. At first, Tom is only taking advantage of it to prepare to cook the little duckling into stew, but by the time the duckling willing decides to do it, Tom can't bring himself to cook the little guy and saves him. Also one of the few episodes that ends with Tom having a happy ending.
Family Guy: Peter pretended to attend Meg's high school to discourage the students from licking toads, but he eventually started thinking he was a real teenager.
Also occurs in the episode "Brian writes a bestseller": Though his original intention was to write trash out of sheer frustration, the work began to garner fame and appreciation from the looked-down-at people and he started to really believe he was a genius, and he had created a life-changing masterpiece.
Subverted on one season finale of Aqua Teen Hunger Force, where the Teens were revealed to be secret agents of some sort and Carl was a secret agent assigned to spy on them. At the end of the episode, he mixes up strip club and liquor store, implying that the real Carl does not share the *ahem* interests of the Carl we've come to know and love. Of course, given what show we're talking about, don't expect this to carry over into next season.
In As Told by Ginger, Mipsy uses her cousin, Thea, to try to influence Ginger to stay at a private boarding school. Thea spends a semester with Ginger, and during the process, warms up to her and admits she felt bad about the deception, but only did so because she really needed the money to fund her shopping addiction. It's not hard to interpret that she legitimately wanted Ginger to stay because she liked her.
In Ed, Edd n Eddy, Eddy decides to dress up as a foreign exchange student named 'Carl', to find out who wrote graffiti about him. When he introduces himself to the rest of the kids, he finds out that they all prefer him, instead of Eddy. Double D (the one who wrote "Eddy is a no neck chump" in the first place) tells the surprised 'Carl' that it's respect, and that he hasn't done anything to provoke a negative opinion, like scamming for pocket change.
In another episode, Edd builds a monster suit for Ed, only for Ed to start believing he actually is a monster and proceeds to go on a rampage through the neighborhood.
My Little Pony: Friendship Is Magic has this happen with Discord of all villains. Princess Celestia charges Fluttershy with redeeming him, and Discord plays along while plotting to exploit Fluttershy's kind nature to ensure his freedom. However, during this, he finds out she genuinely saw him as a friend and her friendship actually means something to him. The end result is Discord reforming for real rather because he can't bring himself to lose the one genuine friend he'd ever made.
Knock Out of all bots does this in the finale movie of Transformers Prime, Predacon Rising. While his personality and motives remain virtually unchanged up until the very end of the film. His assistance (however limited) when facing Unicron's undead Predacon army, and later showing genuine regret when Optimus dies seems to indicate he's genuinely changed.
Some tribal cultures have rituals in which a mask causes the wearer to become the god or spirit it represents.
When you act out a role, it naturally becomes less and less of an act, as seen with method actors and army drill sergeants.
Psychologist Philip Zimbardo cut short his famous Stanford Prison Experimentwhen he realized that he was beginning to think like the sadistic prison guards he was studying. It only took six days out of a planned two weeks for his test subjects to fully internalize their roles; of these once ordinary people, those chosen to be guards exhibited genuine sadism, and those chosen to be prisoners exhibited genuine helplessness and submission.
A Russian Intrepid Reporter, Yaroslava Tankova, went undercover as a Gold Digger to write a series of articles about such women in 2008-2009. In the last article she admitted that she almost wanted to give up journalism and become one.
C. S. Lewis said in the preface to "Screwtape Proposes a Toast" that while lots of people requested a sequel to The Screwtape Letters, for the longest time he refused to write one because even though the original book was the easiest thing to write that he had ever produced in his life, it was a horrific and stifling experience to have to make himself think like Screwtape and basically become a demon.
He also said that those who are afraid that they can't "love their neighbor" should just act as if they did and the rest would take care of itself. He said that the whole point of ritual and formalised prayer was that you could 'dress up' as a saint - and thereby become one.
In World War II, after the Italians turned against the Nazis, the Germans coached an Italian petty thief to pose as an aristocratic Italian general and convince several captured resistance fighters to spill their secrets. He set out instead to be an inspiring figure who'd help the men hold onto their information and their pride. When the Germans executed him for betraying them, he died still maintaining the false identity. This was made into a movie, General della Rovere, in 1959.
ATF agent William Queen spent two years undercover as Billy St. John, a member of the Mongols motorcycle gang, and admits he grew to liking the gang he was in and found them kinder than many law abiding folks he knew. He felt somewhat sorry for turning them in when his job investigating and spying on the gang was over.
Undercover agents and officers undergo extensive psychological testing, and extensive training, specifically to avert this trope. Unfortunately for Pistone, he went deep cover before any of this and had to rely on his own values.
One of the tenets of Alcoholics Anonymous is "Fake It Till You Make It": By forcing yourself to act a certain way even if you don't like it, it eventually becomes a habit.
If a person fakes a smile (or a frown) their mood will be affected accordingly, at least a little bit. Try smiling right now, you'll feel better!
People who freeze their faces with anti-wrinkle chemicals such as Botox are shown to not feel as sad or as happy as other people.
Peter Sellers had said on numerous occasions "There is no 'Me'; I do not exist." As an actor, he became his role and often had a hard time shaking it off afterward.
Robin Williams stays in character off set until the film is done. When he performed the chilling lead role in One Hour Photo, his wife was so upset she told him she would divorce him if he took another role like that.
Hugh Laurie really did develop soreness in his back and leg from constantly limping in his role as Dr. Greg House. He also kept the accent even when flubbing lines.
Christian Bale did interviews for the Batman movies in the same accent that he uses in the movies to avoid those who don't know his other works. Pretty jarring during the MTV Movie Awards when he spoke to Brandon Routh using his natural accent.
Andy Kaufman was a vegan in real life but ate meat when portraying the Jerk Ass lounge singer Tony Clifton because Clifton ate meat.
It is quite common that actors portraying characters who are close friends will also become friends in Real Life.
Cirroc Lofton and Avery Brooks of Deep Space Nine developed a real son-father type relationship away from the set.
The actors who play Sherlock Holmes and Dr. Watson always seem to end up being extremely close friends in real life. Casting for modern adaptations mainly focused on the chemistry of the two leads so they would invoke this trope.
Jeremy Brett and Edward Hardwicke are prime examples: Hardwicke, who played Watson from "The Empty House" onward, would try to help Brett while he was battling bipolar disorder.
The core cast of Boy Meets World (Ben Savage, Danielle Fishel, Rider Strong, and Will Friedle) have all become True Companions in Real Life, much as their characters (Cory, Topanga, Shawn, and Eric, respectively) did on the show.
Christopher Reeve became to be considered as noble a man as Superman - first when he went to Chile under the tyranny of Augusto Pinochet to help some arrested actors despite the obvious risk to his life, and after he became a crusader for the disabled after his riding accident.
The converse of this is sadly also possible. Warren Mitchell and Tony Booth, who played a feuding father- and son-in-law duo in Till Death Do Us Part came to loath each other in real life. Mitchell still cannot bring himself to refer to Booth by his first name.
An aversion is shown in A Bright Shining Lie by Neil Sheehan. US advisor John Vann builds up ARVN officer Colonel Huynh Van Cao as a Blood Knight anti-communist tiger in the belief that this trope would come into effect. However Cao often refused to close with and destroy Viet Cong forces when he had the opportunity to do so, as President Diem had ordered casualties to be kept to a minimum, and the propaganda image the Americans had built up prevented them from acknowledging the flaws in the South Vietnamese military.
A common dating tip for men who have trouble approaching women because of low self-confidence is "Pretend that you've got a lot of confidence. After a while you'll find that you don't need to fake it anymore." Similar tricks may work for socialization in general.