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Amnesiac Dissonance occurs when a good or evil person suddenly remembers their past of the opposite alignment. This becomes the epitome of Man versus Himself (or Herself) as the values and memories of their past self collide with their current self. This can result in a complete Face-Heel Turn or Heel-Face Turn, or give a shade of grey to the character that they didn't possess before. Reincarnation can be substituted as a type of spiritual amnesia.
This is not possession, or merely being brainwashed; this is the self, one's own Good and Evil, conflicting in the most direct way possible. The darkest result is the tragedy where whatever goodness might have been is erased. It requires Heroic Willpower to continue being a good guy when remembering The Dark Side and the powers it enables. Sometimes, though, Redemption Equals Death.
Note, Heel-Face Brainwashing and then coming out of it may lead to this.
This tends to be more the good character remembering an evil past because Amnesiacs Are Innocent, but it's only a tendency. May overlap with The Killer In Me and Alternate Identity Amnesia. Can stem from Amnesiac Resonance: a character who, for instance, realizes his own familiarity with guns and wonders why he used them.
A variation may be that the person never gets their memory back directly, but does find out who they were previously and has to deal with the implications; be they crippling guilt over past evil, or longing for the simple pleasures after petting the dog.
See Identity Amnesia, Loss of Identity, and Amnesiac Liar. Compare Lost in Character.
Contrast with Pygmalion Snap Back, wherein a person (sometimes voluntarily; sometimes not) changes some aspect of their personality at the behest or influence of another, and upon disillusionment the old personality trait is restored with a vengeance.
This is always a huge character spoiler. Please take care before reading these examples.
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Anime and Manga
Happens several times in Angel Sanctuary, subverted with Setsuna and Sara: Setsuna regains some of Alexiel's memories but manages to maintain his identity as a separate person from her, and Sara never regains any memories of her life as Gabriel but played agonizingly straight with Kira.
For the first two seasons of Blood+, Saya goes through this after meeting Haji, and starts to remember when she went berserk in Vietnam and older memories.
Villetta Nu of Code Geass goes through this when her battlefield injuries leave her amnesiac. One of the enemy, Kaname Ohgi, takes her in, conceals her past from her, and keeps her hidden from his comrades. Slowly, she grows infatuated with him...until her memories resurface and she shoots him with his own gun before rejoining her old allies. In spite of this, Ohgi risks his life to confess his love to her, and in the end, Villetta is able to reconcile her identities and marry him.
In Deadman Wonderland, Nagi seems to be a perfectly friendly, polite and kind-hearted widower, whose only wish is to see his child outside of prison. Turns out that's not exactly the case. With the help of a bit of drugs and Mind Screw, he remembers that when he was shown his unborn child's fetus in a test tube, he stewed over it for a week, then went and murdered twenty-two prison guards with his bare hands; he also recalls his general hatred for all of humanity. It's not a pretty moment.
Inverted and averted in Death Note: Protagonist Light gives up his memories of being the mass-murderer "Kira", then his mind wiped self tries to clear his name by joining a task force devoted to capturing Kira. Although he still keeps his intelligence and says that his thought patterns are similar to Kira's, his personality changes to that of a decent person rather than the self-righteous, prideful Well-Intentioned Extremist he was before that would be willing to use the Death Note (the most jarring is the difference in how he treats Misa). Even if he doesn't sympathise with Kira because he wants to clear his name, the personality change was the series' only notable headache. But when he gets his memories back, there's no dissonance - just a Psychotic Smirk. Everything that happened went "Exactly as planned."
In Dragon Ball Goku is shocked to discover he isn't a human with ridiculous strength, a monkey tail, and the ability to turn into a giant ape, he was a Saiyan sent to earth to destroy it. Unfortunately his older brother tries to convince him of this by kidnapping his only son, and Goku got amnesia as a baby so he has no memory of being an evil Saiyan anyway. By the time he embraces his Saiyan side (during his battle with Frieza) he's the only known Saiyan alive so there's no pressure to conform anymore.
In Elfen Lied, when Lucy loses her memories, she goes from being a violent mass murderer to an innocent, harmless (and slightly retarded) girl, Nyu.
After Greed is captured in Fullmetal Alchemist, he is given complete amnesia by his creator Father. When confronted by a former companion, Greed kills the companion which causes memories to start resurfacing. One of the images he sees is King Bradley (who killed his three closest companions) and Greed attacks King Bradley's house before running away.
In Gunnm (aka Battle Angel), Alita/Gally eventually discovers that she was a ruthless terrorist before her body was discovered in the Scrapyard at the beginning of the series. In fact, she's directly responsible for the dystopia she'd been rebelling against.
Though he didn't exactly turn evil, Sho in Guyver had this happen in the infamous arc where he killed his father after said father had been forcibly turned into a Guyver-killing Zoanoid that ripped out Sho's brain. Notably, Sho was affected by this for some time: he built up a mental block about his powers that only subsided when his love of and duty towards Mizuki overruled his guilt.
In the Higurashi no Naku Koro ni manga, Keiichi falls asleep, and forgets he kills Mion and Rena. He wakes up quickly and sees the bloody sight. This is not in the anime or sound novels, though.
In Magical Project S, Sasami's friend Misao has the split personality of Pixy Misa created by Rumia. Since she has no memories of being Pixy Misa, she's completely clueless. Pixy Misa seems to be aware of being Misao, though, and the series often plays this up for laughs, such as when Pixy Misa tricks Sasami into believing she's "kidnapped" Misao (by using a giant screen to cover her transformations, all the while Misao is completely confused as to what's going on). After Misao discovers that she's Pixy Misa and had been fighting her best friend all along, she has a mental breakdown over the conflicting personalities.
In Naruto, nearly played straight with filler character Memna. Formerly a bandit, he became kindly and even heroic after losing his memories. However, the trope falls apart when it's revealed that he lost his memories during a Heel-Face Turn.
In a later episode of Noir it appears that Kirika is being brainwashed. The reality is that her self up to that point was the brainwashed self, and the ritual removes it. In the penultimate episode, Mireille fights not only the "true" Kirika, but attempts to get her "fake" version back.
Mara from Ah! My Goddess, despite being a demon, is shown to be extremely gentle and kind after she loses her memories. Unfortunately for the protagonists, she was holding Keiichi's sister hostage before she lost her memories, making it necessary for them to restore her memories.
In Scrapped Princess, Sim, a cute little amnesiac waif, is taken in by the main characters. She is later abducted by the Peacemakers, ancient humanlike machines out to kill the protagonists, and revealed to be one of them who had been uncompressed from her storage state erroneously. When she is fully uncompressed, she is called 'Cz', has the form of an adult and remembers her original function as the protagonists' enemy, though she retains her 'Sim' memories.
Akira in Eden of the East wakes up naked in the middle of Washington D.C. with a cell phone and no clue who he is or how he ended up there. As he tries to figure out what's going on, he at first gets the impression that he was a terrorist, but it's a bit more complicated than that...
In Fairy Tail, Jellal gets called out for all his past crimes by Erza during the Oracion Seis arc when she's trying to prove she's not going to fall for his tricks again and buy his lie about having amnesia. Except he really does have amnesia, and since neither of them know that he was brainwashed into committing those crimes, and he's actually a good person at heart he's horrified to learn what kind of a person he was.
Teito in 07 Ghostflees the military, abandoning a promising career, when he remembers that Ayanami, one of the top military officers, killed his "father."
Neo Roanoke in Mobile Suit Gundam SEED Destiny comes down with a bad case of amnesiac dissonance once he's taken prisoner aboard the Archangel and meets Captain Murrue Ramius, who was his lover back when he was the heroic Ace Pilot Mu La Flaga. Unfortunately, this and Neo's feelings about the unpleasant things he'd been doing prior to that point are given very little screen time.
Kurando from Popcorn Avatar. When he was little, he was much more energetic and prone to perverted pranks. When he temporarily regresses to that mental age, he makes such an impression on the girls in his class that they continue to be terrified of him after he reverts back to normal.
In Omamori Himari, Yuuto is horrified when some of his memories come back and he realizes that he was once eager to slay demons, instead of befriending them like he does now.
In the anime film Colorful"I", a forsaken spirit that possesses a boy called Makoto, is more vocal and forward then Makoto ever was much to the surprise of his classmates, prompting "I" to wonder what kind of person Makoto was. "I" as it turns out is Makoto.
In the Big Finish Doctor Who audio play Master, the Master is given 10 years of an amnesia-induced normal life if the Doctor agrees to kill him at the end of it. Things get complicated to where the Master has to decide whether to become evil again for the right reasons, or to stay who he is for the wrong reasons.
Also happens in the audio drama The Holy Terror: when Eugene Tacitus remembers that he killed his own son and that the entire fictional world he lives in is designed to torture him for it, he is so overcome with guilt that, despite the Doctor's pleas, he makes the Creepy Child that represents his son stab him with the knife he was going to use to kill it.
There is an instance or two where The Joker, Batman's enemy from The DCU, loses his memories and becomes a regular family man. This self is always consumed by his madness returning.
Marvel loved this trope. Early on in Ultimate X-Men, Professor Xavier mindwiped Magneto and convinced him that he was a baseline human who taught handicapped children and was having a relationship with a human woman (with whom he eventually moved in). It worked...for a while.
Another Marvel example is Taskmaster. It was recently revealed that his Photographic reflex ability comes at the cost of his personal memories. When he's able to remember who he was (A SHIELD agent named Tony Masters and that he's married to the woman that was tagging along with him in the adventure who is also a SHIELD agent) he regrets all the bad things he has done as Taskmaster. Sadly, in order to protect his wife Mercedes, he has to use his ability to its limit by combining every move he had learned along with copying the fighting style of the guy attacking them in order to defeat him, causing him to forget himself again.
Earth-2 Catwoman had been suffering from amnesia during her criminal career. When she recovered, she was willing to go to prison for her crimes. (Later, during a story where Batman sprang her from jail to help him, she revealed that she had made up the amnesia to make her Heel-Face Turn plausible; in reality, she had wanted to quit.)
In 100 Bullets, various characters discover that they were formerly highly trained assassins known as Minutemen who were brainwashed into forgetting their work. As they are awakened to their real memories by various usages of an embedded code word, they must decide whether to return to their old agenda or walk away.
In Sonic the Comic, Super Sonic is haunted for a long time by recurring nightmares of a demonic creature destroying the world and saving him for last. Eventually, he discovers these are actually representations of his past destructive urges, remembering in full that he was once the evil, chaotic Super Sonic. This leads him to refuse to use his powers lest he become corrupted by them once more - indeed, each time he taps chaos energy or his inert powers, he reverts to his crazy self. His desire to not become a demon again ends in tragedy, as he is corrupted by the power of all seven emeralds - while attempting to save his own life nonetheless - and he is promptly merged back with Sonic, seemingly ending the pacifist Super Sonic's life.
In the My Little Pony: Friendship Is Magic fic Past Sins, Nightmare Moon is reborn as a filly as part of a botched spell by a cult seeking to resurrect her as a mare of her own. She regains some of her old memories, leading her to feel guilt and then loses it when she regains all of them as the same cult recast the spell on her to complete her.
In Ditzy Doo: Muffins, Ditzy starts to recover her memories from before she came to Ponyville, and freaks out when she thinks she may have been a mob enforcer who killed a Canterlot guard and his wife. She was actually a secret agent who was trying to take down a griffon mobster, and was too late to warn the guard that the mob was after him.
In the Pony POV Series, Discord was once reborn as the child of a mortal pony named Shady. Bereft of his memories as a God of Evil, Discord grew up loving Shady like any good son, and became best friends with Celestia and Luna (who likewise were reborn to G1 Mimic). Then the memories of his past life returned. Discord resisted returning to his old evil self, but ultimately became a villain again when his evil persona consumed his good one.
It should be noted that the Alicorns did this kind of thing, in order to better relate to the lives they must help. While we only see three instances (two of which were the same person) their personalities can differ greatly. However, it's stated that normally, their two personas merge back together upon regaining their true memories, allowing them to find middle ground between them. In Discord's case, his pre and post amnesiac personalities were so different Discord and 'Dissy' couldn't accept one another as the same being.
Another example is Celestia having been being reborn as an Earth Pony during the Windigo's rampage. She watched her family die and was extremely racist towards the pegasi and unicorns, dying cursing the ones who caused her suffering. It was only after dying she realized shewas the one who caused it all and explicitly requested being reborn like this as punishment.
Played with in Bright Eyes' story in the 7 Dreams/Nightmares collection. While never evil, she was always a bit of a know-it-all with a mild Jerkass streak; both attributes were lost when the disaster that ended G2 society caused her to lose her memory. And to the surprise of her friends and family, she keeps the Character Development even after her memory is restored. Her storyline's Big Bad — the Shadow of Existence of Discord's brother D___t — tries to invoke this trope when she's on the cusp of regaining her memories, by posing as her Enemy Within Cruel Eyes and trying to convince her that her original self was a monster who caused the disaster on purpose. She sees through his lies and defeats him.
It's revealed in the Shining Armor Arc that Minuette is actually the Master in pony form, with his consciousness sealed inside a fob watch. She refuses to give into his attempts to open it and become him again.Like Bright Eyes, after putting up with his attempts to regain control for the entire arc, she manages to destroy him for good by feeding him to the Blank Wolf in the Grand Finale, obtaining a life of her own independent of him in the process (though she may still be a Time Lord)..
Another example, from a Loose Canon followup to the Dark World Series: Fluttercruel's spirit is punished for her actions in life by being sent back in time and incarnated as a pony who ended up being one of her own victims. The grief and agony she experienced at her own hooves finalizes her Heel-Face Turn upon her death and return to the spirit world, as she's forced to face the fact that the ponies she hurt were living creatures, not toys for her to torment.
In the My Little Pony: Friendship Is Magic fan novel Fragments, the pegasus "Sky" wakes up injured, alone in a forest, and totally unaware that he is a Changeling, and supposed to be an enemy of Equestria. It takes him many weeks to discover his true identity, and by that time he has thoroughly and enthusiastically absorbed Pony culture, so he no longer wants to live in a Changeling Hive — even if he could find his Hive anymore, after the defeat of Queen Chrysalis.
Ghost Boy centres around events after Wreck-It Ralph, with the Big Bad of that movie Turbo getting his memory wiped after resurrection, and living with the main cast. You can guess what he ends up finding out.But the trope itself gets notably averted: Turbo actively rejects his evil self, and ultimately ends up killing it for good when it scrounges up a separate body.
Discussed in Fire Emblem Awakening fanfic Pretender, Robin believes that his past self before he got amnesia must have been a terrible person since no one bothered to look for him as he probably went missing and was left for dead in a field.
Films — Animated
The title character in The Iron Giant loses his memory shortly after crashing on Earth (probably when he got electrocuted by the power station while trying to eat it), and is unaware that he is actually a Weapon of Mass Destruction until his built in self-defense protocols start getting activated. When he believes Hogarth is dead, the next army attack seems to undo the dent in his head and his full military programming comes back online (though he still reacts based on self-defense, targeting the greatest threat which is actively attacking him). When Hogarth isn't dead, he helps the Giant remember their time together and that he has a choice in his own actions.
Films — Live-Action
Douglas Quaid, the central character in Total Recall (1990), discovers that before he had his memories rewritten he was Hauser, The Dragon to the movie's Big Bad, and that he had been on a mission to destroy the people on whose side he had since come to fight. Or did he .... ?
Regarding Henry, where Harrison Ford plays an Amoral Attorney who gets shot and loses his memory. He's appalled at what a jerk he discovers he was.
In the Laurel and Hardy short "A Chump at Oxford", while our heroes are visiting Oxford University Stan gets hit on the head and becomes a snob with an English accent, much to Ollie's disgust. Not surprisingly he later gets hit on the head again and returns to his old self.
In Overboard, Goldie Hawn plays a Rich Bitch who loses her memory after falling overboard her yacht. Kurt Russell plays an average joe handyman who convinces her that she is his wife (he's widowed) in order to get revenge for unpaid work on the yacht. The two characters fall in love and when Hawn's character eventually regains her memory she must decide whether to go back to her previous life or remain with her new family.
Notably, she doesn't automatically become nice when she gets amnesia. She's still pretty much a bitch until living a life where everything isn't handed to her teaches her some humility.
The fear of Amnesiac Dissonance drives the suspense in Unknown2006. Several kidnappers and their captives wake up in a vacant warehouse, having succumbed to an accidental gas leak that has caused temporary amnesia. They find clues that some of them are criminals, but don't know which of their own number are the bad guys, and need to figure it out before the rest of the kidnapping gang comes to collect their prisoner.
Seen in X2: X-Men United; Stryker claims that he and Wolverine were partners before Wolverine lost his memory.
Stryker: You were always an animal, Wolverine. I just gave you claws.
Based on the prequel film, Stryker appears to have been projecting his own moral vacuum onto a member of the subspecies of humanity he despised.
Happens in Resident Evil with Spence. Gas released by the Red Queen's defences causes him (and Alice) to lose their memories. He spends most of the film as a good guy but, when he regains his memory, he also reverts to his original personality - an amoral shit whose theft of the T-Virus started everything.
Played with in Dark City: J. Murdoch has no memories, and the only evidence he can find about his past points to him being a serial killer. He's horrified, and soon becomes convinced that it can't be true, that he isn't a killer. Turns out he's right, and the truth is even stranger: Reality Warper aliens had staged the evidence, and implanted everyone around him with false memories—and they've been doing so for years. Murdoch's own amnesia is because he had somehow rejected the latest attempted memory transplant.
Lieutenant Payton in Pandorum is honestly trying to remotely assist Bower in his attempt to restart the ship's reactor. However, when he finds out that he is really Corporal Gallo (he had hypersleep-induced amnesia), he instantly turns into a murderous nihilist.
Liam Neeson's character in 2011's Unknown (aka Unknown White Male) turns out to be a terrorist/mercenary-assassin.
In Robert Ludlum'sThe Bourne Identity, the amnesiac David Webb comes to believe that he is professional contract killer Jason Bourne, which was in fact only a cover assigned to him by the CIA before the incident that caused his amnesia. When the Big Bad comes to realize that something of this nature is occurring, he begins setting Webb/Bourne up to reinforce this belief.
This is played quite differently in the movie adaptations of the Bourne novels; prior to his amnesia, Webb/Bourne had in fact been trained as an assassin, if a government-sponsored one. The amnesia works as something as a mental-reset button, as he'd been brainwashed into becoming the assassin. As a result, post-amnesia he is The Atoner.
The entire plotline of K. J. Parker's The Scavenger Trilogy, although Poldarn quickly figures out that he probably won't like what he remembers.
The problem isn't just that he has issues with who he was before he lost his memories. It's also that the amnesia fades over time, so he repeatedly regains memories too late to stop himself causing a tragedy and/or realises too late that the tragedies he purposefully caused were committed upon his former friends and loved ones, giving him issues with what he did as an amnesiac. Even more Amnesiac dissonance is (mostly) averted by the fact that he doesn't remember the horrible deaths he has died in previous incarnations except in dreams. He is (possibly) both the final reincarnation of everyone in the novel and the god Poldarn who is fated to cause the Apocalypse without knowing he is the god Poldarn. Making him both culprit and victim in different incarnations of every atrocity in the series.
Cal Leandros gets bitten by a monster that gives him amnesia in Blackout. He immediately figures out he's a morally ambiguous 'killer' and rolls with it, but once he gets reintroduced to his life he is very disturbed by a photograph of himself from before. Most of the book deals with his struggle between wondering if he should stay amnesiac and moral, or try to regain his memories and become who he was before. When he realizes the latter will allow him to protect Niko better, he barely even hesitates restoring himself.
At the start of Darksong Ember regains her memory and is forced to face not only the knowledge of her illness and impending death, but also the personality she created to deal with it. This personality becomes known as Dark Ember, and represents the forces of Chaos. They try a Split Personality Merge, but discover that they are too incompatible.
P.G. Wodehouse's novel The Indiscretions of Archie does this for laughs: Archie befriends a man who has lost his memory during the war and, horrified, suspects that his name may be Lancelot.
At the beginning of John C. Wright'sThe Golden Age, Phaethon learns that he is suffering from Laser-Guided Amnesia and is told he has committed horrible offenses. A Neptunian urges him to flee to have his personality repaired, pointing out that his self-chosen name shows that he is not by nature as acquiescent as he acts.
In the third book, The Golden Transcedence, Daphne reveals to Helion that so far from supporting the Horators' attempt to stop Phaethon, in his missing hour of life, he had pledged to support Phaethon.
Happens in the EVE Online novel Empyrean Age: A high-ranking, slave-keeping Amarrian official suffers amnesia due to a botched assassination attempt. He is found by a Ragtag Bunch of Misfits, which includes Minmatar members, who naturally react to his presence with revulsion. While he eventually resumes his position, he keeps the nice guy persona he developed during the story.
In a short story by Vivian Vande Velde, a young prince wakes up in a field staring into the eyes of a witch, who tells him perhaps this will help, and leaves. He struggles to survive in the nearby city, selling everything he has on him and eventually working for a living. Finally, he comes across some people who recognize him and take him home. Due to his complete amnesia of anything before, and the fact that he now understands how difficult other people have it, he's a much nicer person. Everyone who knew him before keeps complimenting him on his niceness in a way that's not quite complimentary. Even worse, his Arranged Marriage fiancee has the same eyes as the witch who cursed him, a fact he tries hard not to think about too much.
A somewhat similar situation comes up in Diana Wynne Jones' Castle in the Air, where it turns out that a character had been given amnesia and memories of a different identity to teach him a lesson.
Self-inflicted in John M. Ford's short story Erase/Record/Play, in which the scientists experimenting on prisoners in a concentration camp give everyone - victims, guards, and tormentors - the same experimental memory-wiping drug, and mix themselves into the general population to avoid punishment when the liberators come. They can't be coerced or tricked into revealing their guilt, because even they don't know if they're guilty.
In The Candy Shop War, Nate and his friends are given a Blank Slate—a magical food that will cause whoever eats it to lose all their memories and become, well, a Blank Slate—and are told to use it on a rival magician. They can't bring themselves to do it, but Nate holds on to the food anyway. But when it becomes apparent that there's no way to stop the main villainess from drinking from the Fountain of Youth and becomming an unstoppable Child Mage, he crumbles the slate into her goblet of magic water... thus turning her into a harmless and sweet-natured little girl.
In Evan Hunter's novel Buddwing a man wakes up in a park with no idea who he is. He creates a name for himself based on seeing a Budweiser truck and an airplane and goes searching for who he is and what has happened to him. At the end he realizes that his wife committed suicide because of his dickishness and the shock gives him amnesia again and the story starts all over again. In the movie "Mister Buddwing" he realizes that his wife is in a hospital, not a mortuary, and he goes to her and apparently reconciles.
In Larissa Ione's Rogue Rider when Reseph remembers what he did while he was Pestilence he suffers a sanity break as the pure evil of the actions he remembers are such an antithesis of his true nature.
The episode "Passing Through Gethsemane" centers around a mind-wiped Serial Killer who lives as a monk in a religious order. Upon discovering his past, he's aghast. How can he pray for forgiveness when he doesn't even know his sins? Ultimately, he decides the only way he can atone is through death. And so, despite his superior's pleas that he accept the mercy of a new life, he allows himself to be crucified by the families of his old victims. In an ironicTwist Ending, the leader of the lynch mob is sentenced to mind-wipe, and joins the same religious order.
In the episode "Divided Loyalties" Lyta Alexander arrives on Bablyon 5 to tell captain Sheridan that someone onboard the station is a sleeper agent and that only by sending a specific word into their minds to activate the agent can they find out who it is. Turns out it's Talia Winters, who's sleeper personality seems to be as chaotic and malicious as Talia was formerlly calm and helpful.
Buffy the Vampire Slayer: It's written into Angel's curse that every time he's subjected to a Heel-Face Turn, he gets about 30 seconds of amnesia before the memories of his past evils return all at once, sending him into his usual guilt spiral.
Subverted in the case of Connor, who didn't get a full restore, but a vague remembrance like a dream. As the major impression is that they were very unpleasant, he seems happy enough with who he is now.
In the Doctor Who episode "Utopia", the Master hides from the Time War by transforming himself into a human being and erasing his memory, becoming the mild-mannered, philanthropic Professor Yana. His original memories are stored inside a watch which, when he opens it decades later, restores his memories to him - and in an instant, he turns against everyone he'd been working with as Yana and hatches a plan to conquer the universe.
Played for Laughs and Lampshade Hanging in an episode of Due South where Benton, in a state of amnesia, reacts with total bemusement to the other characters' explanations of what he is normally like, and the quirks that they have all by then gotten used to, like his living in an unfurnished apartment where he sleeps on the floor. ("Why am I living like this? Am I being punished?")
Inverted in Heroes, when Peter Petrelli wakes up in a cargo box with total amnesia. He resists learning about his past for the longest time, because he fears that he'll find out he's really evil. Naturally, pretty much everyone who hears this—cast and audience alike—laugh their asses off at this possibility.
Later played straight when Matt Parkman uses mind control to make Sylar (the big bad) forget his past and think he was somebody else. When shown his real past he flips out, and the mind control means he still can't remember it properly.
In an episode of Hustle, The Mark discovered the con, then came down with Easy Amnesia. The team decided this was an opportunity to run the scam again without making the same mistakes, but when they saw how horrified he was at his own business practices they realised they were breaking The Code; conning an honest man. (It eventually transpired that he'd either regained or never lost his memory, and was setting them up. However, their refusal to con him at the end left him reluctant to follow-through, and may have caused a genuine Heel-Face Turn, but is left ambiguous.)
This is the entire premise of Christina Applegate's show Samantha Who?
The Stargate SG-1 episode "Past and Present" had Daniel Jackson fall in love with an amnesiac named Ke'ra, who's a doctor working to reverse a global pandemic that has the entire population to suffer amnesia. It's later revealed that she is actually a de-aged Linea, also known as "The Destroyer of Worlds", who created the very plague in the first place to regain her youth and the amnesia was an unforeseen side-effect. When her cure causes her to start regaining her memory, she tries to kill herself but Daniel stops her and reinfects her with the virus, which unfortunately erases her memories of him.
The Stargate Atlantis episode "Michael" features previously unknown Lieutenant Michael Kenmore having nightmares of being a Wraith. As it turns out, he was subjected to an experimental treatment to turn wraiths human, giving him a grudge against both the wraith and humanity, both of whom he later attempts to exterminate.
In the 1996 made-for-television movie Sweet Dreams, Alison Sullivan, played by Tiffani-Amber Theissen, awakes from a coma with amnesia. She speaks to various acquaintances from her life to uncover her past, discovering that she had not previously been a nice person, and begins to realize that her amnesia is a result of someone's attempt to murder her because of her misdeeds. She foils them, and then decides to stay the nice new version of herself.
In the Red Dwarf episode "Back To Reality", the crew wake up from the virtual reality game they were playing, and discover that their real personalities are very different from the people they thought they were. Dave Lister, who likes to think he's a good guy who will usually do the right thing, discovers that he's really a brutal fascist officer; Arnold Rimmer, who thinks he's better than Lister, discovers that he's really Lister's less successful brother; Kryten, who thinks he'd never harm a human being, discovers that he's capable of murder; and the Cat, who defines his whole existence by his sense of style and good taste, discovers that he's really an awkward, buck-toothed, fashion-deficient Nerd. Subverted when it turns out this is all a hallucination created by the Despair Squid, and their "game" personalities are their real ones after all.
An episode of Criminal Minds had a serial killer attempting to escape police, only to fall several stories down and end up in a coma. He awakes years later, with no memory of his former life or his actions. Most people believe he's faking, but his amnesia is sincere... Until his memories begin returning. He escapes and is tracked to the park he worked at as a ranger, the police believing him trying to kill one more time. In actuality he dug up a previously-unfound body to confirm whether his memories were real. He turns himself in on discovering this, admitting to all his crimes in exchange for life rather than a death sentence due to his sincere regret for his actions.
One episode of Medium centers around a former serial killer whose modus operandi was to hire a prostitute, smother her with a pillow after having sex, and bury her in the desert. But one night his plan goes awry when the woman's pimp breaks into his house as part of a planned robbery, and the killer is shot in the head during the ensuing scuffle. When the prostitute visits him in the hospital, she finds that he has amnesia, and remembers nothing about his murders. Once he is discharged from the hospital, he continues his life minus the murders; the woman leaves her life of prostitution and eventually the two end up married. Despite learning all this from the former prostitute, Allison continues to pursue the issue so the bodies can be found. When pressed, the former killer seems to vaguely remember the murders, and it is implied that he leads the police to the bodies. It's never made clear when the memories began to come back, how many of them came back, or even if he ever truly forgot.
On Dollhouse, Echo gradually comes to realize that Caroline, the original personality in her body, wasn't such a good person, and is no longer sure if she wants her old memories back. This may have been a response to the audience finding Caroline, who was a radical member of an Animal Wrongs Group, to be a rather unsympathetic heroine.
Although, as Adelle notes, Caroline isn't evil—-she's an idealist (which, Adelle also notes, can be worse). Echo is Not So Different from Caroline, but comes off more sympathetically.
In The Outer Limits (1995) episode "Blank Slate", an amnesiac is being helped by a woman he met while they are being chased by unknown people. Every so often, he gets an injection of liquid that appears to hold his memories, remembering more and more each time. In the end, he is revealed to be the evil boss of the people chasing them and uses the same procedure to erase the woman's memories.
Happened to Divatox in the most infamous episode of Power Rangers Turbo, the one where the rangers get baked into a giant pizza. When she loses her memory, she also loses all piratical aspects of her nature, and becomes a mildly surly (but good natured) employee at a pizza place.
An unusual variation occurs in The Sarah Connor Chronicles episode "Allison from Palmdale." Cameron's processor begins to glitch due to damage sustained earlier in the series, and she loses her sense of "self." She also begins to recall memories of a girl named Allison, who looks exactly like her, who in reality was a resistance fighter that her appearance was modeled after and she interrogated for information. Cameron begins to think she actually is Allison, and begins to act like her, reciting memories of parts of her life and expressing human emotions. Its isn't until the end of the episode that she remembers who she really is and reverts back to her normal programming.
Averted in Kamen Rider Kiva. Wataru and Shizuka befriend a large, cheerful man who Does Not Know His Own Strength, nicknaming him "Dai-chan" ("Mr. Big", essentially). When he recovers his memories, it turns out that he's Rook, The Brute of the Checkmate Four, who spends most of his time engaging in random acts of murder for fun. Recovering his memories causes him to pretty much go back to the monster he was before, except for a rather weird deathbed conversion-type thing where, in his final appearances, he decides to do good deed in the hopes of getting into Heaven.
Another aversion is in Kamen Rider Decade in which Tsukasa is revealed to be Leader of Dai-Shocker, he takes it in stride once his memories return to him when speaking to Tsukikage.
The "Dead Head" episode of Human Target features a money launderer who contracts amnesia on his way to meeting Chance and the team for protection. This leaves them the job of protecting someone without knowing who he is, who's trying to kill him, or why.
The Shadow Line teases this with Jonah Gabriel, who is implied to have been a Dirty Cop before he lost his memory in contrast to the good cop he is afterwards. Ultimately a subversion, however. He was a good cop all along; all the apparent evidence of his corruption turns out to have been part of an investigation into actual corrupt officers.
The TV movie In the Shadow of Evil is about a cop who develops amnesia while on the case of a serial killer whose pattern indicates he will kill again in a month. Towards the end of the month he has regained enough of his memory to realize he's investigating himself.
In Xena: Warrior Princess, Callisto is eventually redeemed by being turned into an angel, which includes having her memories wiped clean. Despite this, Gabrielle at first refuses to trust her, thinking she's just putting on an act, and cites the many atrocities Callisto did over the years. The newly sweet and innocent Callisto is horrified and refuses to go back to how she was (thankfully, she never does). In the next episode, Xena gets her memories wiped clean and becomes sweet and innocent. She's horrified to learn about her past, but eventually accepts her memories back so she can remember how to fight.
In Community, resident Jerkass Chang shows up with memory loss dubbed "Changnesia" and comes off as a much nicer guy who intends to make up for the mistakes he made in the past. Since he's faking though, it's averted.
Played with in the Star Trek: The Next Generation episode "Frame of Mind": Commander Riker finds himself in an alien Bedlam House. The wardens tell him that he has gone crazy and has brutally stabbed another person to death. But Riker doesn't remember having ever done this, and is of course reacting quite aghast. (It is even implied that he never was the respected Starfleet officer he considers himself, and any memories of his time on the Enterprise are just part of his delusion.) In the end, all this turns out to be just an elaborate ruse by the aliens, as an attempt to extract information from the mind of the Starfleet officer.
He seems to be aware of this on some level, judging by the opening comic to the White Treatise sourcebook (in which Arianna suggests finding out about their past lives, and he isn't really all that keen).
As of Scroll of Exalts' write-up of him, Word of God states that he remembers snippets of his past life: not all of those particular moments, but enough to know that the Usurpation may have had some justification, and that his former incarnation's wife might want him dead.
Le voyageur sans bagage (Traveler without luggage) is a Jean Anouilh play about a thoughtful, peaceful man who lost his memory in World War I and spent years in a psychiatric institution, oblivious to his identity. When his true family comes to reclaim him, he discovers that their missing son was a violent, borderline sociopathic egotist. Soon, though, the evidence that this man was him is undeniable. Disgusted, he denies it anyway, lying in order to leave with another, much nicer family he met earlier in the play.
Happy Birthday, Wanda June by Kurt Vonnegut is a comic example of this trope. Major Sigfried von Koningswald is an evil Nazi sadist who, now dead and in heaven, is baffled by his previous actions. He struggles to explain them to the audience...or to himself.
von Konigswald: Orange juice! I killed a man with Orange juice?
In The Granstream Saga, the game alludes to a dark lord who once reigned a century ago. Near the end of the game, we discover that this dark lord is in fact a previous incarnation of the game's hero Eon.
Tales of Innocence invokes the reincarnation variation of the trope with every Avatar ingame. Luca, having been the great Overlord Asura, is constantly attacked by friends and foes from his old life. Meanwhile, both Luca and Iria go into brief Heroic BSOD when they regain their memories of the roles their past lives played in the destruction of Devaloka/Tenjo. All the other party members also comply to the trope, to a slightly lesser extent.
Terra from Final Fantasy VI suffers from a variation from the start. Kefka had put a slave crown on her and used her powers for all sorts of casual slaughter with her being utterly oblivious about this. Once it comes off and people mention what she's done, she comes down with massively crippling guilt for a large part of the game. Combined with her fears of being less-than-human, she makes a very effective woobie.
Dissidia: Final Fantasy mirrors this by having Terra learn that in a past cycle, she was brainwashed and forced to fight on the side of Chaos.
And Duodecim, the prequel, plays through that cycle, revealing that it was Vaan who helped snap her out of it.
Kuja in duodecim was this close to joining the good guys until Kefka ruined his plans and manipulated him into dying in a battle with Lightning. First thing when Kuja was revived in the next cycle, Kefka put it in his head that he loathed Zidane and wanted nothing more than to kill him
Jecht is also a victim of this trope. In the original Dissidia, he's one of the warriors sided with Chaos and acts as The Rival for his son Tidus. However, he really isn't all that villainous, and is a gruff but good-natured guy. Near the end of the story, it's revealed that he actually used to be on the other side in previous cycles; but was captured and Brainwashed to be used as a pawn in The Emperor's schemes.
Duodecim reveals that he fought alongside Yuna for the Warriors of Cosmos in the last timeline, while Tidus was brainwashed into serving Chaos. Ultimately, Jecht sacrificed himself to save Tidus's life, and the Warriors of Chaos retrieved his body just before he could die in order to reprogram it.
Ghost Trick spends a lot of time setting this up, displaying the seemingly nefarious doings of pre-death Sissel and making the protagonist wonder if he was really that bad of a person. Of course, the man in red is certainly a monster... but Sissel's not the man in red.
This happens with Garcian Smith at the end of the chapter "Smile" in Killer7. In his last life, he was the assassin Emir Parkreiner, sent to kill the Killer7. He succeeded, but after killing his mentor Harman Smith, he committed suicide out of grief. Hasidic Harman, the godlike being who had manifested as Harman Smith and led Emir to do these things, resurrected Emir as Garcian Smith, with the souls of the other six Killer7 agents bound to him as alternate personalities, along with Master Harman (yet another manifestation of Hasidic Harman).
They do, however, at least give both choices a motive for doing so.
The Legacy of Kain series averts this trope, but only temporarily. The vampire-wraith Raziel discovers that he and his brothers used to be vampire-slaying priests. At first he embraces his former humanity, but upon traveling into the past, he discovers they were just as bad as, (if not worse) than, the vampires they hunted. Raziel renounces and kills his former self, setting the stage for his eventual resurrection as an amnesiac vampire.
Human Raziel: "You're a righteous fiend, aren't you?"
Wraith Raziel: "Apparently I am..."
This is the major plot twist in Lufia (Estopolis in Japan), and one of the earliest examples of the trope in a game plot.
Much of Zero's story in the Mega Man X games comes from villains attempting to resurrect his "true" personality as a ruthless killing machine; there has been much fan speculation that Zero was responsible for the deaths of the original cast of the Mega Man (Classic) games while in this state.
The aforementioned theory was Jossed fairly recently; Word of God stated that Zero was not responsible in any way, shape, or form for whatever happened to the cast of the original Mega Man games, even as his "original" self.
Zero suffers this again in the transition between the X and Mega Man Zero series. While he stays a hero in between both series, his memory was lost during hibernation, including one crucial detail: that the body he was inhabiting was a duplicate.
In Persona 3, Ryoji's only reason for being is to serve as the vessel by which Nyx will destroy the world. In a subversion, despite the fact that it is against his will, he accepts it as inevitable and gives the Main Character the option of killing him (and erasing SEES' memories of the Dark Hour) to spare them the agony of having to watch the Fall unfold before their very eyes.
It's also revealed, if the right actions are taken, that the protagonist's first self was responsible for possibly more evil than the rest of the incarnations put together prior to becoming The Atoner. In fact, that turns out to be the reason for the immortality thing: Whatever the First Incarnation did, it was so bad that a lifetime of doing good would not be enough to atone for it. The solution was to have many lifetimes, but due to the amnesia thing that didn't work so well.
Alex Mercer of Prototype hunts down and kills dozens of people and killing several thousand in the crossfire in a combination of a Roaring Rampage of Revenge and investigation of the Infection's release and his own transformation, only to find out that the real Mercer was not only one of the very scientists he'd been tracking and killing, but also solely responsible for both. Funnily enough, this means that he was less evil as a sociopathic Humanoid Abomination; the original Mercer only cared about himself, while Virus Mercer slowly starts to grow a conscience.
The game also plays with the trope in that Virus!Mercer is not actually Human!Mercer, as Human!Mercer actually died and Virus!Mercer was created from his corpse. The reason he has no memory isn't trauma, its that they were never his memories to begin with.
In La Pucelle Tactics, two of the characters have lost their memories two years ago. Both of them are now demon hunters on the side of light. Turns out, one of them is actually the "Dark Prince", the emissary of the in-game equivalent of the Devil, and was dead set on destroying all humanity.
Shining Force 2: When the young boy Oddler is left blind and amnesia-stricken by battle wounds, The Hero takes him into his party, protecting the youth from devils that have been hunting him for some reason. Near the end of the game, though, the truth comes out: Oddler is Odd Eye, the most powerful general in the Big Bad's devil army! Though he still remembers traveling with The Hero, his eyes have been opened and his duty is clear. Now they must fight.
In Snatcher, protagonist Gillian Seed is an amnesiac police agent who is assigned to take out the identity-stealingandroids. However, by the game's end, he finds that he and his wife were both scientists who worked on the Snatchers. Though to be fair, his wife was captured to do it while Gillian was The Mole for the CIA, investigating Russia's secret projects.
In Super Robot Wars Advance, Amnesiac Axel Almer, who serves a stint as protagonist, is actually The Dragon of the Big Bad and the Mad Scientist's lover. He comes to grips with this and proceeds to betray his former comrades, who thought he was just being a really awesome spy. Not a spoiler, as the other protagonist's route warns you of this immediately.
This is also the stint of Cobray Gordon in Super Robot Wars Alpha 3. Certain event causes him to lose his memories and join the team. This gets more complicated as he's under the threat of The dead Ingram Prisken trying to take over his body.
Mai Kobayashi is a double case of this. As Levi Torah, she tried to resist the Judecca's control, pleading for someone to rescue her. Then, when the Alpha Numbers/Original Generations save her, she forgets all about the Ze Balmary, only for memories of Levi to come back and try to take control of her again.
Amnesia: The Dark Descent: One of the true horrors of the game is realizing what a depraved monster the player character Daniel was before he gave himself amnesia. No wonder he chose to forget, even though it would make killing Alexander a lot easier if he knew what he was supposed to do and why.
In Twisted Metal Black, Roadkill's driver is an amnesiac who came to in the wreckage of a gangland bombing, and finds himself covered with one of the gang's tattoos. He enters the tournament in the hopes that Calypso will restore his memory. In his ending, it's revealed that he was an undercover FBI agent, and saved dozens of lives in the bombing incident. He is, in fact, a hero... and he's standing in front of one of the world's most wanted criminals, who shoots him dead.
Another character in the game, Preacher, believes himself to be possessed by a demon that slaughtered his congregation during an exorcism gone bad; he wants Calypso's help to clear his name and reveal the truth to everyone so he can fight the demon. Calypso delivers the truth, but it's not what Preacher wanted to know... that there was no demon, the "exorcism" was just a baptism, and Preacher is a psychotic multiple-murderer. He doesn't take it well.
the white chamber has Arthur reveal to Sarah that she was the one who murdered the entire crew. Whether she redeems herself or not is dependent on the player's actions throughout the game.
Cave Story subverts this. Several NPCs recognize Quote as "a soldier from the surface", or make references to squads of war robots that came to the island ten years ago and massacred the Mimigas. The obvious conclusion for the player (and several in-game characters) is that Quote was one of those killer robots—rather unsettling since Quote is currently trying to save the remaining Mimigas. But, if you complete the sidequest to save Curly Brace and restore her memories, then she remembers that Quote was comrade-in-arms ten years ago. And unlike all the other combat robots, they hadn't fought the Mimigas; their mission had been to destroy the Demon Crown.
Inverted several ways in Fire Emblem Awakening with Morgan, the son/daughter of the Avatar from the future. Whereas the other twelve children all come from a future where Grima plunged their world into chaos, Morgan - an amnesiac - is implied to be from another timeline, which itself is noted in all of his/her endings. The subversion comes from the fact that both male and female Morgan exist in the Future Past DLC, which is nearly identical to the timeline the other twelve children are from, only even bleaker. Here, both are devoted servants/the implied children of Grima. There is no hint in-game, though, that either one is from the Future Past timeline.
It gets even more complicated when one takes into account that Morgan can be the son/daughter of any character in the game, including the children characters themselves. Since an Avatar/child pairing is impossible in the future timeline due to the Avatar's fate in the original timeline, this only brings up more questions.
World of Warcraft: This occurs during the starter quests for the Death Knight class. You, the Death Knight player, start the game following orders from Lich King & pals. You run about destroying a town, slaughtering its townsfolk and torturing its guards. Then you're given an order to kill a hostage NPC, but when you confront him/her, he/she turns out to be an old friend of yours who reminds you of your past before you became a pawn of the Lich King—when you were a hero. After you finish the NPC off, you begin your transformation into an Anti-Hero.
In Diablo III, one of your partners is part of a zealous organization that does this to its recruits - former criminals who agree to having their memories wiped so that they may seek redemption. You meet him when you're dungeon crawling in a place where one of his companions is hiding, having just turned traitor. Turns out the guy betrayed his organization after gaining the ability to regain his lost memories, and had been horrified to realize that he was just some Average Joe who signed up for a job. Your partner eventually does the same thing, finding the same thing. Subversion! ... Maybe. It's unclear whether the organization actually does take in former criminals that way.
Played with strangely in Trauma Team. CR-S01 is a surgeon committed to saving lives who was seemingly a bioterrorist behind an attack on Cumberland College prior to his amnesia. However, despite the fact that he can't remember how he did it or why, he's fully aware of this fact — it's actually his knowledge of what he might have done before, absent any of the memories that drove him to it, that motivates his Heel-Face Turn. Then finally outright subverted when it turns out he was never responsible for the attack in the first place, and he was never a villain.
Initially, Overlord doesn't even provide a framework for this trope—the game begins with your being disinterred and declared the Overlord, and apart from indications that you were quite evil your past is treated as unimportant. You are informed, however, that the seven heroes who oppose you previously defeated not you, but "your predecessor." You were the eighth hero, fallen in battle and left for dead. How much of a shock this is depends on how you've been playing.
In I Have No Mouth and I Must Scream, one of the main playing characters is an elderly German scientist called Nimdok who has a failing memory. The Big Bad of the game, mad and omnipotent supercomputer AM, sends him to confront his past... where it is revealed that he was working for the Nazis, directly under the command of Josef Mengele in a death camp, doing barbaric experiences on dozens of innocents. On top of that, it's hinted he was a jew who gave up some of his people to survive. Apart from that, Nimdok is a kind old man who is horrified by what he discovers in the camp and feels sorry for the detainees here.
Played with in Primordia. Due to repeated self-induced memory wipes Horatio doesn't remember his original identity, his only clues being a broken-down warship, an unexplained, preprogrammed hatred towards Metropol, and a desire to fly. Fairly early in the game, various characters start addressing him as "Horus", which, according to Memorious's information kiosk, was an Urbanian weapon sent against Metropol and shot down by Goliath on the way. However, if you decrypt Horatio's files near the end of the game, it turns out that Horus — the warship — actually won against Goliath, but refused to kill the last humans in Metropol, and willingly crashed in the desert after uploading a chunk of its AI into its robotic servitor, who took on the name "Horatio". It is left entirely up to the player whether the unlocked destructive powers should be embraced, ignored, or used selectively.
The hero of the Infinity Blade series, Siris, is nothing like his past self as Ausar the Vile. Prior to having his memory erased, Ausar was a monster who brought nothing but ruin to the world. Siris is horrified by the man he was and seeks atonement for the deeds he no longer remembers. Highlighted in the expansion "Ausar Rising" when Siris faces a soulless clone of himself with Ausar's memories. Siris denounces "Ausar" as a monster and slays him with extreme prejudice.
In Jigoku-hen, multiple characters do not recall certain members from absent series in this game. For example, when the eponymous Aquarion EVOL makes it debut, ZEUTH and ZEXIS feel a stinging sensation, forgetting about the original Aquarion cast.
Tanya, who is the android love interest from the science fiction visual novelBionic Heart, learns that her creator used a serial killer's brain in building her, which explains why she has century-old memories. Unsurprisingly, she has a Heroic BSOD from the revelation.
Trace from TwoKinds. Interesting in that the only person not aware of his past is Trace, nearly everyone else is well aware of who he is/was and are openly terrified of him. It's gotten to the point that Trace has decided that he's better off not knowing who he was.
MSF High: Students at MSF High can surpress painful memories as part of their 'second chance'. If these memories are discovered, this can occur.
In Fleep, Jimmy is rather horrified to infer that he used to be a terrorist, and that the building he's trapped in was collapsed by a bomb he set off. What's interesting is that he never actually remembers any of this—so he ends up inferring what he did well before he figures out why he did it.
Hector: Animated Armor and Minion with an F in Evilturned good from A Modest Destiny, were at some point "resurrected" by the resident vampire lord, Fluffy. The only thing he can remember is that it was his own sister that killed him, and she is also a vampire. It is later revealed that she didn't do it personally, she had Fluffy bind Hector's soul to the armor in order to save him. Apparently, Hector was, at some point, a psychopath with such issues that even the baby-eating Fluffy was disgusted by him. When Hector got the offer to be returned to life in a real body, he refused, as he was afraid that he would go back to being whatever he was before.
In The Gamers Alliance, Ronove recovers his memories during the siege of Vanna and remembers that he used to be a Dreadlord of one of the demon hordes. After this realization he leaves his human friends behind, retakes his former position in the horde, starts acting like a seemingly cruel Manipulative Bastard as most demons do, but he also still seems to harbor some feelings for his former companions in the Alliance who he is now forced to oppose. He shows some of his quirky habits from his amnesiac cuckoolander days (such as his love for cake and sand gnome legs) but it's now mixed with his former dutiful yet cruelly efficient persona which has evolved into something more manipulative and vengeful because he's now fully aware of who betrayed him and caused his amnesia in the first place. He even keeps lampshading his sudden personality change every now and then, further cementing the fact that the different sides of Ronove coexist and that he hasn't set aside everything from his amnesiac days.
In Legion of Super Heroes animated series, there are two ShapeShifters, one on each side, who undergo processes to forget themselves and become one of the other side's members in order to gain intelligence. Chameleon Boy ends up stuck as Persuader before finally remembering who he is. And Superboy ends up revealing he's actually Ron-Karr in the process and is shocked to discover he'd forgotten who he really was.
In the Lilo & Stitch: The Series episode "Amnesio", the experiment of the week erases peoples' memories. Lilo, Stitch, and Gantu all get zapped and try to reassemble their pasts together; they don't come up with much that's conclusive about Lilo or Stitch, but reckon Gantu must have been a cop. So they become very good friends, and don't worry all that much about their memories-until Lilo learns that there's a way to reverse the effect, and learns the codeword. Gantu, meanwhile, has learned that he was not a very nice guy. He's quite vehement that he doesn't want to go back to being a jerk-until Lilo says the codeword anyway, and he remembers the one bit of context his amnesiac self didn't, viz. he loves being a jerk.
In a second-season episode of Superman: The Animated Series, villainous cyborg Metallo turns up on a volcanic island with no memory of himself; he saves a young girl's life and does other good deeds, but eventually he remembers his battle with Superman and turns evil again.
In Transformers: Beast Machines (the sequel to Beast Wars), Megatron had brainwashed two of the Maximals and given them entirely new identities. Upon recovery, Silverbolt became The Atoner, and Rhinox decided to stay evil and competed with Megatron.
Also from Transformers, the character Flip Sides from both G1 and Transformers Animated, is a decepticon who has a double-life as an Autobot—in G1 she's a teacher, in Animated she's a pop star. The catch is, while she's an autobot, she does not know or realize that she is a decepticon spy. Talk about conflicting moralities.
In an episode of Aladdin: The Series, Jasmine lost her memory due to a magic rose and Abis Mal convinced her that she was evil. This backfired when Jasmine became a Dark Action Girl and decided the idiotic Abis Mal was beneath her.
In the Generator Rex episode "Rabble", Rex is hit hard with this as he meets up with three old friends of his - who he doesn't remember at all - who are stuck working for a crime boss named Quarry. It turns out that in a former life, Rex sold out his friends to Quarry in the first place, and Quarry uses this fact to turn Rex's old friends against him.
An antiheroic version: in one episode of DuckTales, Scrooge lost his memory and was lost on the streets without a penny to his name. Eventually he moved in and began a romance with his unknowing accountant's extremely working class mother, and when she told him about Scrooge McDuck's employment practices he reinvented himself as a socialist crusader against a man he saw as a Corrupt Corporate Executive. At the end of the episode he regained his memories and had no recollection of what happened, but the protest he unknowingly began forced him to improve worker rights.
In an episode of Young Justice, the team wakes up in the Biyalian desert with their memories of the past six months erased. This turns Superboy into a mindless berserker (he's not even six months old), Kid Flash and Artemis start flirting with each other and even hold hands right before their memories are restored, and Artemis believes she is there because her father wants her to kill Kid Flash.
In the Adventure Time episode "Ghost Princess", the helpful male ghost named Clarence who's been helping Finn and Jake investigate Ghost Princess's death, and who has also been falling in love with the princess, turns out to have been the guy who killed her in life. Of course, in life they were Star-Crossed Lovers, so that helps...
Subverted in Teenage Mutant Ninja Turtles 1987: When Shredder gets amnesia the first thing he does is save a man's life, making it seem like this trope is being put into effect, but it turns out his evil instincts are still there when he finds the idea of building an explosive so he can use it to hold the city hostage fun.
In Chip 'n Dale Rescue Rangers, a Tap on the Head gives Dale amnesia and Fat Cat's cousin Maltese de Sade uses it to convince Dale that he is actually the criminal Ramdale. Ramdale manages to be surprisingly efficient and nearly manages to defeat the rest of the Rescue Rangers.