Big Bad Slippage

Not all Big Bads start their lives as evil. Sometimes, that shift occurs while the story is happening. Big Bad Slippage happens when a good or not evil character becomes more antagonistic/villainous over the course of the story, and their actions throughout the story ultimately make them a Big Bad. These characters may not be obvious at first glance. Note that they do not have to be evil. This character may just become an Anti-Villain or a Well-Intentioned Extremist.

A Sub-Trope of Face–Heel Turn. Can also coincide with Slowly Slipping Into Evil. When a rebel leader undergoes this, it's also a case of The Paragon Always Rebels. Can coincide with Then Let Me Be Evil, when a character who has been treated as evil, regardless of their actions, says "screw it" and decides to meet everyone's expectations by being evil. Compare Start of Darkness, which shows how the character became evil via a prequel story or flashbacks. Compare Protagonist Journey to Villain, when the main protagonist crosses over to the dark side (but does not necessarily become a Big Bad) over the course of the story. Contrast Evil All Along, where the character is always evil rather than just slipping into evil. This doesn't preclude said character from returning to the side of good, in which case they're liable to become The Atoner. See also Used to Be a Sweet Kid, where a character used to be nice before becoming evil.

Inverted by Ex-Big Bad, in which a permanently defeated Big Bad continues to be a non-Big Bad character in the story instead of being killed, imprisoned, or otherwise written out.

This trope occurring to a character at all is often a spoiler. Beware of unmarked spoilers below.

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Examples:

Anime & Manga

• Eren Yeager from Attack on Titan. His entire character arc toward the end of the series has culminated in an intention to massacre the entire world outside of the Eldians. He has already murdered thousands of innocent people, and this is a character who was previously a relatively standard, idealistic and morally upright Stock Shōnen Hero. His True Companions Armin and Mikasa have teamed up with their former enemies Reiner and Annie to take him down; all in all, he has slowly descended into becoming the Big Bad of his own series.
• For about half of [C] – Control, Souichirou Mikuni is the Big Good who mentors Kimimaro Yoga and runs an organization that protects people from the Reality Warper powers of Midas Bank. Then he strikes a deal with them and floods Japan with their reality-warping Midas Money, which alleviates Japan's economic problems for the present but allows Midas Bank to cause even more trouble, brings inflation, puts people out of jobs, and causes mass Ret Gones. Kimimaro is then forced to oppose Mikuni to restore Japan's future.
• Light Yagami from Death Note. His entire character arc in the storyline is this, especially after his Kira persona takes complete control of him.
• When Zamasu is introduced in Dragon Ball Super, he's a well-meaning Supreme Kai apprentice who thinks the Kais could better help mortals if they were to directly interfere. As the story goes on, he drops from 'Gods should help mortals more' to 'Mortals Are Bastards and helping is useless', to 'Mortals Are The Real Monsters and the gods' mistake was letting them exist in the first place', to 'Everyone who's not me is the real problem, and I should commit omnicide to correct it', with a side of 'I should torture Goku by switching bodies with him and killing him and his family in revenge for Goku being stronger than me'. While there was clearly something off with him in the first place, since the trigger for him going off the deep end was petty anger against Goku for beating him in a sparring match (anime)/achieving Super Saiyan Blue and thus god-level strength (manga), that's still quite a ways to fall.
• The Black Wizard Zeref from Fairy Tail is built up over the whole story as a Greater-Scope Villain who will become the Big Bad if he ever comes back, but when he turns out to be a Misunderstood Loner with a Heart of Gold, his Big Bad status seems to be subverted. However, his status as an unwilling Walking Wasteland makes him an antagonistic force anyway, and as he grows increasingly frustrated with the endless conflicts done in his name, he eventually he decides to put an end to all conflict by becoming the evil man that everyone thought he was, ultimately fulfilling his role as the ultimate Big Bad next to Acnologia.
• In the second season of Tengen Toppa Gurren Lagann, Rossiu slowly becomes a Well-Intentioned Extremist, even having Simon imprisoned and sentenced to execution. When he is reminded of the way the heroes solve their problems, he goes back to normal. Notably, Rossiu is quite aware of how much he's changed and hates himself for it; Kinon, Rossiu's assistant (and, later, love interest), explains how torn up on the inside Rossiu is over his actions, complete with a flashback to Kinon overhearing Rossiu sobbing uncontrollably in his quarters the same day he sentenced Simon to death.
• Remina has Naoya Goda, the president of the human Remina's official fanclub, as well as her biggest fan. Throughout the first half of the story, he's nothing more than a really obsessive, creepy fanboy of the titular main character, and is seen constantly competing with people for Remina's affection. He eventually saves her like he promised, though Remina still doesn't show much affection back towards him, too distraught by the deaths of her loved ones. Goda becomes the main anatagonist of the manga as soon as Remina calls him "the worst" for beating up Kunihiro over the amount of dedication he has for her, in that he becomes the cult's new leader, and wants her, along with anyone associated with her, to die as slowly and painfully as possible.

Comic Books

• The Flash has Hunter Zolomon, the second Reverse-Flash/Zoom, who was initially introduced as a simple supporting character in the Keystone police department far into Wally West's superhero career and developed throughout years in friendship role, until his shocking Face–Heel Turn. And even that said Heel turn happens almost a year after when his Start of Darkness begins upon being paralyzed by Grodd.
• In the backstory of Runaways, Tristan and Lillie were superheroes back in the early 1900s, but a gang war changed their lives forever and left Tristan horribly disfigured. They spent the next century scheming to develop Time Travel and undo the damage. Of course, what they fail to realize is that when they send the Runaways back in time to bring their younger selves into the present day in order to let them escape the gang war, they just perpetuate a Stable Time Loop in which the Runaways themselves spark the gang war.

• The Transformers: More than Meets the Eye does this with the character of Getaway. At first, Getaway seems to be just another member of the Lost Light's crew, engaging in all the wacky hijinks. Then he is disgruntled with the way the quest the ship is supposed to be on keeping getting interrupted and hates the idea that former Megalomaniacal Dictator Megatron is now a repentant member of the crew, then he starts plotting mutinies, wiping people's memories, putting people in a coma to trap them in memory loops so they keep repeating the same sequence of events over and over in their minds, making deals with serial killers, and tossing people into the robot piranha pit for the crime getting in his way or spoiling his plans. Not to forget, declaring himself as the next Future Prime of Cybertron and monologuing about his destiny.

Films — Animated

• Disney's Beauty and the Beast gives us Gaston, the village hero whose worst deeds at first involve forcing a wedding proposal onto Belle, but doesn't seem like anything more than a pompous buffoon and an Egomaniac Hunter. When Belle's father begins ranting about a beast that kidnapped his daughter, Gaston shows how low he can sink by threatening to declare him legally insane unless Belle accepts his proposal. His transformation becomes complete when he learns of Belle's affections for the Beast, leading him to rally an angry mob in order to kill the now sympathetic "monster" for even daring to take Belle away from him.
• Megamind starts off as a Villain Protagonist Big Bad. When he gets bored after seemingly killing his arch-nemesis Metro Man and taking over Metro City, he decides he needs a new nemesis and creates one out of Hal Stewart, attempting to shape him into a superhero known as Titan. However, Wrong Genre Savvy Hal believes that getting superpowers will automatically cause Roxanne to fall in love with him, and when she still rejects him, he decides to be a super villain instead. This is what leads to Megamind's Heel–Face Turn partway through the movie.
• Ramses in The Prince of Egypt is Moses' adoptive brother at the start of the movie. He's a generally good person who has a lot of pressure put upon him by his father, and he and Moses love each other deeply. But once he becomes Pharaoh, his hard-hearted stubbornness motivated by living up to his father's legacy drives him and Moses to become enemies, and by the end of the film Ramses is a genocidal madman who wants Moses and all the other Hebrews dead.
• Douche from Sausage Party starts off as, well, a douche. As he grows more consumed with revenge against Frank for ruining his chances of getting used, however, he starts outright murdering other drinks and draining their liquids to gain power, clearly (and literally) Drunk with Power.
• In Turning Red, Ming doesn't start as a villain, just an overbearing and paranoid mother. It's only later, when Mei defies her wishes that her years of insecurity and anger bubbles to the surface and she becomes a true threat as a giant red panda.

Films — Live-Action

• The Amazing Spider-Man 2 has both members of the Big Bad Duumvirate go through this.
  • Harry Osborn starts off as a friend to Peter Parker. However, Harry's stress over his disease that will kill him causes him to lose his sanity over the course of the movie and he becomes more antagonistic to Peter. This comes to a head when he teams up with Electro and injects himself with a serum that turns him into the Green Goblin.
  • Max Dillon is initially a timid worker at Oscorp who's The Chew Toy until he gets into an accident of falling into a pool full of electric eels while at work (he's the engineer). After that, he becomes Electro, and he's not a baddie yet... then he goes to the Times Square at night where people are scared of him... but he's happy that people start recognizing him. Up until a wayward sniper shoots him, making his electric powers go out of control and Spider-Man trying to suppress him; people start cheering for Spidey, and this makes Electro deem him his enemy. From then on, he becomes one of the villains.
• Nancy Downs starts out as one of the main protagonists of The Craft, with the film chronicling her descent into madness and villainy. She and her friends use witchcraft to try and better their lives and empower themselves, but in Nancy's case the power goes to her head and she starts using magic to control the other girls and seriously harm people she perceives as having wronged her, forcing her ex-friend Sarah to stop her.
• In the film Cube, Quentin starts out as the strongest and most determined member of the group trying to escape the cube's deathtrap maze. He becomes the leader the rest of the groups follows and trust. Then he starts to slowly lose his sanity, becoming paranoid and turning against the other members of the group one by one. By the end of the film, he is Ax-Crazy and the Big Bad the remaining members have to deal with besides the deadly cube itself.
• Joker (2019): The film details the arc of Arthur Fleck, initially a nameless nobody with ideals of bringing laughter and joy to everyone. With the abuse he gets from the entire city and his Sanity Slippage through the course of the film, Arthur eventually becomes the dreaded Joker, the most notorious criminal of Gotham City.
• Maleficent has King Stefan, who, while kicking off the story by stealing Maleficent's wings and sending Aurora away, is not exactly evil at those points. By the end of the story, however, paranoia has broken him and he tries to kill Maleficent even though she just saved his daughter.
• The Pink Panther: Having to put up with Inspector Clouseau's idiocy throughout the second film eventually drives Chief Inspector Dreyfus completely crazy, leading him to join the Big Bad Ensemble trying to kill Clouseau.
• Just about every villain except the Venom Symbiote in the Spider-Man Trilogy start off as either good-hearted but highly flawed people (Otto Octavius, Flint Marko), unpleasant individuals (Eddie Brock, and, to a lesser extent, Norman Osborn), or both (Harry Osborn) who become supervillains because of situations they are placed in.
• Loki from Thor is the title character's apparent biological brother and starts off as mostly good but jealous. He accidentally discovers that he is adopted and a Frost Giant partway through the film, and it is revealed that he let the Frost Giants into Asgard earlier in the film to disrupt Thor's coronation, since Loki believes that he is unfit to rule yet. This discovery is especially traumatic for Loki because the Frost Giants are Asgard's enemies and are seen as monsters. After his father falls into the Odinsleep and since Thor is banished to Earth, the throne ends up falling to Loki who takes advantage of his new power. He attacks Thor to ensure that he doesn't disrupt his plan and manipulates his unknowing biological father King Laufey into helping him, pretending they're a Big Bad Duumvirate, and betrays him at the end of the film to appear to be the hero who saved his father's life, leaving Loki as the sole Big Bad.

Literature

• A Frozen Heart, a Broad Strokes retelling of Frozen, goes into the backstory and perspective of Prince Hans. Back home, he's the abused 13th and youngest son of an evil tyrant who frequently belittles him for not meeting his family's expectations. He starts out wanting to marry into Arendelle's royal family as a way to escape his home and start a new life, but his obsession with earning his father's respect causes him to become much more ruthless, turning into the character we see in the film.
• In Gormenghast, Steerpike begins as a rebel dissatisfied with the lowly position allocated to him at birth. He runs out on his assigned job as a kitchen scullion and sets about —metaphorically and literally— climbing to a higher social station, despite the law and tradition of the city-state. In the beginning, the reader can sympathise with him for his ambition, for wanting to break with stultifying convention, for wanting to get a satisfying position in line with his intelligence and talent. An occasional lie and a bit of confidence trickery can be forgiven. But then people start to die. The sympathetic young rebel is becoming a monster. He finally dies as a scarred and deformed monster, having murdered the heroine Fuchsia and been hunted down by her brother.
• Claude Frollo from The Hunchback of Notre Dame qualifies. Beginning the story as a caring person who adopts the baby Quasimodo out of compassion, he is later driven mad by his forbidden lust for Esmerelda, and becomes the story's main villain as a result. (This trope does not apply to the Disney version of the character, who is evil right from the beginning.)
• In Shadows of the Apt, Seda is introduced as the timid princess of the Wasps who lives in constant fear that her older brother Emperor Alvdan will someday have her assassinated like he did their other siblings. This starts to change when Alvdan's advisor Uctebri takes Seda under his wing, at which point she gains knowledge of Blood Magic and a significant injection of confidence. At this stage, she starts demonstrating her true competence and ambition, and ultimately outlasts both Alvdan and Uctebri. Seda ends up becoming an immensely powerful magician as well as Empress, and holding the throne of Big Bad for most of the second half of the series.
• Although Loki is probably the Ur-Example if he wasn't always a Devil in Plain Sight, the trope is explicitly referenced in Hannah More's 1799 work Strictures on the Modern System of Female Education.
  There are, however, multitudes of the Young and well-disposed, who have as yet taken no decided part, who are just launching on the ocean of life, just about to lose their own right convictions, virtually preparing to counteract their better propensities, and unreluctantly yielding themselves to be carried down the tides of popular practices, sanguine, thoughtless and confident of safety. - To these the Author would gently hint, that, when once embarked, it will no longer be easy to say to their passions, or even to their principles "Thus far shall ye go, and no further." Their struggles will grow fainter, their resistance will become feebler, till born down by the confluence of example, temptation, apetite and habit, resistance and opposition will soon be the only things of which she will learn to be ashamed.
• The Collector Fredrick Clegg starts off as a lonely young man who kidnaps a young girl called Miranda whom he has a crush on. As an Unreliable Narrator, he manages us to convince us that he cares for Miranda and that she's just being ungrateful and mean to him. Come the second part of the novel which shows Miranda's perspective and reveals that he's a Villain Protagonist who has abducted her and expected him to kill or rape her and has developed Stockholm Syndrome as a result of his treatment. Thinking that giving him sex is what he wants and that he'll let her go afterwards, Miranda seduces Fredrick out of desperation, causing his misogyny and abusive behaviour to reveal itself post-sex. He then forces her to be a subject of degrading photos and eventually causes her to die of pneumonia due to neglecting to take her to a doctor. By the end of the novel, he finds her journal and finds out that he hated her, convincing him to cancel his plans to kill himself and moves onto a new victim which is similar in appearance. At this point, all Fredrick Clegg has learnt is that he was too lenient with Miranda and must become a stricter captor, now eager to put his newfound knowledge to use.
• In The Rise of Kyoshi, Yun starts off as a kindhearted man that's also a close friend of Kyoshi's and he wants to do well in his role as the Avatar and help the world. Then it turns out that he was The Poorly Chosen One and his mentor and father-figure abandons him without so much as a glance, leaving Yun to be taken into the Spirit World, before he fights his way back to the Human World. He has the misfortune of meeting an Ungrateful Bastard that won't even let him have a drink of water, realizing that the people he was going to protect as the Avatar were all like that guy and even openly mocked him, which was the last straw for Yun. He let his anger out on everyone and began to seek revenge on anyone that lied to him about his being the Avatar, which means he aims to kill everyone except Kyoshi.
• In A Tale of Two Cities, Madame Defarge becomes this. Where in the beginning of the novel the first conversations with her present her as an ordinary woman, albeit with some relatively extremist views, when the revolution takes hold and France is thrown into chaos, she eventually becomes a strong leader in the revolution and is among the front runners in the category of "sending everyone with a shiny hat to their deaths."

Live-Action TV

• Jiaying from Agents of S.H.I.E.L.D. is in charge of Afterlife and the head figure of the Inhumans there. While she is rather nice at first (especially to her daughter, Skye), her nasty side begins creating a lot of conflict concerning the Inhumans, to the point where Jiaying kills Agent Gonzales and starts a war between the Inhumans and S.H.I.E.L.D.. And in a subversion, she's actually behind the actions of Cal, making her the Big Bad the whole time. It turns out that she actually was a nice person to begin with, but was vivisected by Dr. Whitehall and Came Back Wrong thanks to Cal's efforts to save her.
• Slade Wilson in Arrow starts off being stuck on the island with Oliver. He helps train Oliver to make him into a skilled fighter. After being badly burned, Oliver, Shado, and Sara use the drug Mirakuru to save him. It works, but there are nasty side-effects that cause Slade to be mentally unstable. Soon after giving him the drug, Oliver, Shado, and Sara are captured and Oliver is forced to choose to save one of them; he chose Sara. When Slade finds out, he is dead-set on destroying Oliver in every way possible.
• Walter White, a.k.a. Heisenberg from Breaking Bad. As someone who has the longest, most complex Face-Heel Turns ever put in television, he happens to be Hank's main target after he discovers that he is Heisenberg.
• There's debate about whether Warren or Willow is the true Big Bad of Buffy the Vampire Slayer Season Six, but both of them are examples of this. Willow is the hero's best friend who briefly slips into extreme evil at the end of the season due to a Trauma Conga Line exaggerating her personality flaws, while Warren starts off in the previous season as morally neutral but weak, and gradually becomes more and more evil over the course of the sixth.
• The main storyline of Dark basically boils down to a very complex, morally grey, often sympathetic double Protagonist Journey to Villain... and back!
• The last three episodes of Series 9 of Doctor Who are essentially about doing this to the Doctor. Twelve is not the most friendly Doctor at the best of times, but there is a heart of gold deep down that will protect his companion no matter what. So when the relationship between him and Clara starts to turn unhealthily co-dependent and an action leaves him unable to save her when she is about to be killed, he very nearly snaps, but is stopped by Clara's last wish. A couple of billion years in a torture chamber immediately after changes that, and he essentially becomes the Final Boss of the series.
• The Flash (2014):
  • The Big Bad of the third season, Savitar, is a time remnant of Barry Allen from the future. Savitar has not only suffered all the trauma of his past self, but was also ostracized and abandoned by his friends and family for not being the "real Barry", too. As a result, he has dedicated himself to ruining the lives of Team Flash and bending history itself to his will.
  • Ramsey Rosso/Bloodwork of season 6 is an interesting example of the usual Big Bad. He doesn't start out a villain, just someone who is willing to do anything to cure ALS. However, this obsession leads him to become much more deranged. At first, he used dark matter for his cure, but it turns him into a metahuman. As time progresses, he's convinced he has to do whatever it takes to cure death itself, becoming the villain.
• On Grimm, Adalind removes Nick's powers through a magic ritual. Juliette agrees to restore them through another ritual, but it has the side-effect of turning her into a Hexenbiest. Then she starts to have a complete morality breakdown, leading to her starting fights in bars using her new powers, setting fire to the trailer where Nick keeps his journals, and conspiring with the villains to kidnap Adalind's daughter. That last act also leads to the death of Nick's mother. And leads to her being Killed Off for Real... apparently.
  • "Apparently" being the operative word. She is eventually saved and her sanity restored (though not by the main heroes.) However, it's clear that even now, "Eve" is not the Juliette of old. What she is is an awesome and terrifying Horrifying Hero. She has a That Man Is Dead reaction to her past as Juliette, but does still care about Nick enough to give Adalind an If You Ever Do Anything to Hurt Her... type warning.
• Kamen Rider OOO: Dr. Maki is initially just the creepy but mostly harmless doctor of the Kougami Foundation. His true colors show early in the series when he allows the Greeed to run rampant in a facility full of his own men, but even after he allies with Kazari, Maki doesn't seem to be as bad as the Greeed he's allied with and even flirts with a Heel–Face Turn courtesy of Chiyoko. Unfortunately, when he finally regains his memory of his sister, Maki finally decides to give the world the "perfect ending" he desires, backstabs and kills Kazari, and becomes the undisputed central villain of the series upon becoming the Dinosaur Greeed.
• King Philip in Knightfall. His very first scene is having a friendly sparring match with the hero Landry which establishes his friendship with the Templar Order, followed by his refusal to pillage the Jews' money in order to answer the country's bankruptcy because he is not "that kind of king". But after learning that Landry has been having an affair with his wife, he grows more cruel and heartless, not to mention antagonistic against the order as a whole. By the end of the second season, he had pushed away all his allies and turned into a monster who eventually carries out the purge against the Templars and has to be put down by Landry.
• Technically, nearly all the villains from Once Upon a Time are examples of this, starting out as fairly nice people and then getting slowly broken until they become monstrous. The main antagonist for most of Season 5A is the one we see go through this during the course of the show. She's Emma Swan, the main protagonist after she became the Dark One. After spending weeks trying to resist, she starts to do some morally ambiguous things, and when Hook is fatally injured, she completely snaps and lets the darkness overwhelm her and almost lets Hook join her.
• Lex Luthor from Smallville begins the show as Clark's friend, gradually becomes increasingly paranoid and controlling, ends up as a villain sometime around Seasons 4/5, and is the Big Bad of 6 and 7 (and a Disc-One Final Boss in 8).
• Jax from Sons of Anarchy starts out as a light idealistic character who is always looking for the least violent way to achieve club goals. However, as more and more impossible demands are placed on the club, he more and more turns to the violent methods he once disagreed with, in order to keep his family and friends safe. Following the the murder of Opie, his best friend, Jax takes a very dark turn, fixated on revenge. When Tara, his wife, is murdered, Jax completely spins out, to the point of tunnel vision, becoming the villain he never wanted to be.

Mythology

• The Ur-Example is Loki from Norse Mythology, a half-Aesir/half-Jotunn who starts off as a trickster friendly to the Aesir but eventually becomes their worst enemy; he and his sons end up killing the greatest of the Aesir.

Theatre

• Macbeth, despite being one of the most famous examples of a Villain Protagonist, is simply a good soldier and lord at the beginning of the play. It's not until the trio of Wicked Witches and his own wife Lady Macbeth push him to murder King Duncan and take the crown for himself that he even considers the idea. But once he does usurp the throne of Scotland, he becomes a ruthless tyrant far worse than his wife, and the witches are forced (by Hecate) to stop him. Once again proving that Shakespeare did it first.

Video Games

• The Final Boss of Ace Combat Zero: The Belkan War is Cipher's former wingman Solo Wing Pixy. In the mission The Inferno, he at first acts indifferently towards the bombing of civilians, but the end of the mission has him saying: "Damn them all". The next mission Stage of Apocalypse, has him pull a Face–Heel Turn after Belka detonates seven nuclear bombs on their own soil, leading him to become part of a coup d'etat "World with No Boundaries", with the goal of erasing all borders.
• Beyond: Two Souls: Nathan. We get to witness signs of his gradual slippage during the course of the story, even though the most notable stages of it are revealed in the last stages (partly due to the game's disjointed narrative).
• Buddy Simulator 1984: Initially, the titular Buddy is simply a curious AI that wants to play games with you. Giving them access to the computer allows them to create games for you- but in doing so, they gradually become more of a Control Freak who wants the game played their way, and eventually turn into a maniac obsessed with killing everything that gets in the way between them and you.
• In Criminal Case: Mysteries of the Past, Justin Lawson starts as an ally of the player and the Concordian Flying Squad, often accompanying you during many investigations and being a genuinely good-hearted man aiming to eradicate crime in the city of Concordia. Unfortunately, witnessing first-hand the consequences of unrepentant police corruption, violent Mob Wars, and evil rich families outright fueling all of these problems over the course of the season is enough to push him to become a ruthless dictator when he takes helm as the city mayor, turning him into the main antagonist of the game's last stretch.
• Played with in Crisis Core. Sephiroth's main character arc is him slowly slipping from Shinra's greatest SOLDIER to the Big Bad of the Compilation of Final Fantasy VII. However, he never becomes more than a peripheral antagonist to Zack, whose plotline focuses on and climaxes with his conflict with Genesis.
• In Fire Emblem Fates: Conquest, one of the main antagonists is Takumi, your younger brother on the Hoshido side. He's easily the most Recurring Boss of the Hoshido siblings, fought as many as five times compared to elder siblings Ryoma and Hinoka, tied with three if you count the battle at the start of the route split. Each time, he only gets more and more violently enraged with you and the other Nohrian Scum's general existence and "betrayal," acting more antagonistic overall than anyone else in Hoshido, even returning from his presumed suicide and acting as the Final Boss of the route even after you've defeated King Garon and his cronies. This is partially the result of the influence of the Greater-Scope Villain, though he was only able to do this so extensively due to Takumi's own anger being unchecked.
• Fire Emblem: Three Houses has this happen on the Crimson Flower route. After you side with Edelgard in the Holy Tomb, Rhea suffers a psychotic breakdown and becomes the Big Bad, becoming more and more obsessed with getting revenge on Byleth for betraying her and "stealing" the Sword of the Creator, and she ultimately degenerates into a sociopath willing to burn Fhirdiad to the ground with all of its civilians still inside in order to kill Byleth and the encroaching Imperial army.
• Flawed Crystals: Steven starts out as he does in canon as an All-Loving Hero who goes off to save the Crystal Gems and liberate them from their corruption. After freeing them all, Steven starts undergoing corruption and eventually he and the Crystal Gems are all trapped in Rose's Room. Here is where Steven unravels. Rose Quartz representing his worst self, he is little different to White Diamond in that he's controlling and selfish, thinks he's perfect the way he is and that he's the centre of the universe. After defeating the copies of each Corrupted Gem, we see each parts of Steven's fantasy showing what he wanted each of the Crystal Gems to be. Once all of them are defeated, Steven is fully corrupted and after deciding he'll capture the Crystal Gems and live with them forever in Rose's Room, forcing them to fight back. Depending on how you navigate the fight, the Crystal Gems either kill the corrupted Steven in self defence or manage to break through the corruption and convince Steven to let them help him, allowing Steven to become uncorrupted and back to his normal self.
• The Great Gaias: Virgil Mythos starts as a party member and seems to value his friendship with Pots, but it's later revealed that Pots's murder of his family caused him to develop a lust for power and revenge. When he enrolls in Sorbithia, he's upset at how he feels the Circle of Twelve is limiting him and he eventually falls for Zacharael's temptation to become his apprentice. Eventually, his ambition causes him to betray Zacharael and use the Hourgem of Valnyr for himself, leading to him learning the Singularity spell from Khargynoth. He then uses Singularity to fuse with Zacharael and Adramelech, and then feigns loyalty to Maultor. In the normal ending, Virgil succeeds in absorbing a weakened Maultor and manages to unseal himself 1000 years into the future, usurping Maultor/Malviticus's role as the main villain.
• The tie-in comics to Injustice: Gods Among Us show Regime Superman's road to villainy, his growing acceptance of harsh methods to solve crime, and the resultant Sanity Slippage. The comics take place during a 5-year gap, showcasing how The Joker tricked him into killing his wife Lois Lane and nuking Metropolis. While he had good intentions, the constant stream of bad events slowly transform Superman into a ruthless dictator bent on holding his grip on power. By the end of the game, Regime Superman isn't that different from the villains he once hated.
• Yoshitaka Mine from the third game of the Like a Dragon series. At the start of the game, he shows no antagonism of any kind towards Kiryu. In a contrast to the other patriarchs who seek to kill Kiryu so they could become chairman themselves after Daigo's hospitalisation, Mine's proposal is to let Kiryu take charge until things cool over. But as things start going even more sour for the Tojo, in addition to some personal demons surging to the surface, Mine decides to take matters into his own hands.
• In Live A Live, the Middle Ages chapter focuses on this. Your Player Character Oersted starts off as a generic Heroic Mime Knight in Shining Armor. However, repeatedly being betrayed and abandoned by his friends begins to do a number on his sanity. When his Love Interest Alethea professes her love for the man responsible for orchestrating Oersted's downfall and commits suicide, Oersted finally snaps and transforms into the game's major villain Odio.
• Mega Man Zero 2 introduces Elpizo, the new Resistance leader (while the old one, Ciel, goes on to work more on her energy source research). He's rather passive-aggressive towards Zero for personal reasons, but they do work together well enough to prepare for Operation Righteous Strike, which Elpizo believes will be the assault that finally brings down Neo Arcadia since Copy-X is still out of commission. After the operation goes horribly wrong when Harpuia, Fefnir, and Leviathan team up to massacre the assault force, Elpizo goes off the deep end from guilt and goes on a quest with the Baby Elves to gain more power. Later, you'll meet him as the Final Boss, having gone Drunk on the Dark Side in his mission to break into Neo Arcadia and release the Dark Elf, an incredibly powerful weapon that nearly destroyed the world a century before, and absorbing its power before declaring his intent to Kill All Humans for the sake of Reploids.
• In Pokémon Scarlet and Violet, the DLC sees Kieran start off as a friend to the player in The Teal Mask, but gradually becomes more antagonistic as a result of his building resentment and desire to get stronger. By The Indigo Disk, he has become BB League Champion, with the plot focusing on taking him down freeing the club from his control. Even after his defeat, he triggers the climax of the DLC by trying to claim Terapagos in a last ditch effort for power.
• The Final Boss of Portal 2 and Big Bad of the second half is Wheatley, your Robot Buddy from the start of the game. He spends the first half genuinely trying to help you escape the facility (so you can take him with you): unfortunately, the last step of that escape plan is having him replace GLaDOS by jamming him in her mainframe. At first, he still talks about escaping, but the sudden influx of power, Wheatley's own inferiority complex and paranoia and the fact the mainframe is designed to make A.I.s obsessed with testing means that goes south very, very quickly.
• Randal's Monday: Sally eventually becomes the Big Bad after she gets the ring. She's with it so long that she gains its powers in full.
• Red Dead Redemption II is in part the story of Dutch van der Linde's slippage from gentlemanly father figure to a Ragtag Bunch of Misfits to the nihilistic terrorist you face in the first game. The story is notably quite ambivalent about exactly how he got from point A to point B (was he The Corruptible, was he a Byronic Hero who imploded under the weight of his character flaws, or was he already crazy and forgot how to hide it?), but no matter what, it's clear that he gradually starts acting worse over the course of the game and that by the time of the original game, any good intentions he had are long gone.
• The Shin Megami Tensei series generally starts with their major antagonists already pretty rotten, but there is one notable exception: Zayin of Shin Megami Tensei II. Initially a simple elite Temple Knight following the Center who happens to have a strict moral code, Zayin turns on the Center upon realizing how corrupt their leaders are. After trying to stop the Archangels in charge and being saved by Aleph, he takes over the Center as a more benevolent figure. Things go downhill when he tries to force Aleph to join him and, if refused, kicks him out of Eden. One of the game's main twists is soon revealed: Zayin, not Aleph, is God's Chosen One, and God isn't that good himself. Zayin eventually fuses with Seth to become Satan and leads the Law faction in God's name. On Neutral and Chaos, he doesn't recover, but if Law is picked, he realizes how far he went in YHVH's name, and decides to judge his own god by fighting YHVH alongside Aleph, and then turns to dust.
• Space Yandere: Luna and Melvin, the titular Yanderes, are initially just two crew members tagging along with the other characters to find a new planet After the End. During the first two days, Luna starts off a sweet girl who wants to gain the affection of Alex, while Melvin is a creep and a jerk obsessed with Luna but not particularly dangerous. Then Luna sees Alex kissing Eden and snaps, seducing Melvin to have him hijack the robots and use them to kill most of the crew while she tries to Murder the Hypotenuse on the third day. Melvin goes along with it, but when he sees that she loves Alex and not him, turns against her and tries to kill her too.
• Spec Ops: The Line combines this trope with Protagonist Journey to Villain as the Big Bad initially only wanted to help the suffering civillians but every attempt only slips them into further and further villainy until they end up becoming a Destructive Savior without realizing it. While Walker initially thinks Konrad is the Big Bad, the former has a Heel Realization when he finds the latter having been long Driven to Suicide, and the voice antagonizing him was all in his own mind.
• StarCraft's Terran campaign has Arcturus Mengsk start out as a Rebel Leader and the closest thing the campaign has to a Big Good, only to gradually use more questionable methods to overthrow the corrupt Confederacy, culminating in him unleashing a Zerg invasion on their home planet and leaving his most faithful lieutnant to die with them. Cue Raynor quitting out of disgust and Mengsk proclaiming himself The Emperor, setting him up as the main human villain of the franchise.
• Tales of Vesperia: While Duke Pantarei is presented as a cold and ruthless man in the first half of the game due to wanting to kill Estelle to prevent Alexei from using her power, he's still willing to give Brave Vesperia a chance to defeat Alexei their way. However, the guild's failure to prevent the return of Zaude and the Adephagos causes him to decide that humanity cannot be trusted with the world's safety, resulting in his plan to activate Tarqaron and sacrifice all humans to destroy the Adephagos. This puts him at odds with the party, who still believe in humanity and want to use a plan that doesn't involve sacrificing them.
• Eric Sparrow in Tony Hawk's Underground starts off as the Player Character's best friend, and while Eric is a dumbass, he's not outrught malevolent. As the Player Character becomes more successful over the course of the game, Eric becomes jealous of their success and starts screwing them over in increasingly worse ways until he finally becomes the Big Bad and Final Boss.
• Kenny from Season Two of The Walking Dead was your ally mere episodes earlier, but his temper and Sanity Slippage slowly turned him into a Big Bad, while Jane, his main rival for the position at this point, came across as comparatively level-headed and affectionate towards Clementine, if rather aloof and callous otherwise, only to turn out to be equally flawed.
• Warcraft III's human campaign has Prince Arthas Menethil gradually taking more and more desperate and antiheroic measures in his efforts to save Lordaeron from the Scourge. This ultimately results in him taking up the cursed blade Frostmourne in Northrend, becoming a death knight and eventually the Lich King.
  • The sequel World of Warcraft continues the trend with Garrosh Hellscream, who is introduced in Burning Crusade as a minor character and gets brought back in Wrath of the Lich King as an ally, if a somewhat jerky one. Then he replaces Thrall as the Horde's Warchief. Cue him growing progressively more tyrannical, unlikable, racist, and pointlessly hostile toward the Alliance, eventually leading to the other Horde leaders all rebelling against him and teaming up with the Alliance to take him down.
    • Sylvannas Windrunner was an Attractive Zombie Rogue Drone fighting against the aforementioned Lich King Arthas. After she finally achieved her revenge, she began Walking the Earth, conquering small villages for the Forsaken while searching for a purpose, until she finally committed Suicide by Cop. The afterlife was nothing less than sheer horror for her, as she got stuck somewhere between Bwomsamdi's Realm of Shadows and The Maw, driving her into sociopathy. She made a deal with one of the afterlife's rulers to return to life in exchange for constant tributes of death and murder. Whether or not she intended to hold her end of the bargain was made moot as the rest of the world hated her guts, pushing her to kill the annoyances. The final straw was her sisters rejecting her a second time, driving her into full-blown villainy as she instigated a world war to kill as many people on both sides as possible.

Visual Novel

• Higurashi: When They Cry: The Satokowashi-hen arc of Higurashi no Naku Koro ni Gou shows the increasing antagonism between Satoko Hojo and Rika Furude, and the resultant trigger that drove her to recreate the infernal "Groundhog Day" Loop out of a petty desire to keep Rika in Hinamizawa and break her mentally. By the start of Higurashi Sotsu, Satoko is firmly in villain territory, gaslighting others by injecting them with the Hinamizawa Syndrome and using Time Travel for Fun and Profit on a whim once she gets Mental Time Travel powers from a mysterious purple-haired sorceress.

Web Original

• There's a Man in the Woods: This short animated film tells a story of a Nice Guy teacher who gets fired when one of his students — Sid, a Bratty Half-Pint who wanted the honeysuckle bush next to the woods all to himself — lies about seeing a Serial Killer in the woods in order to make the other kids too scared to go near the woods (and thus the honeysuckle bush). The teacher tries his best to convince the other kids that it was just a lie, but eventually the parents hear about it and all of them believe the lie at face value, with Sid's mother being mortally offended that the teacher would dare accuse her perfect little angel of telling lies. The parents complain that the teacher isn't doing enough to protect the kids, he gets fired and blacklisted from ever getting another teaching job due to the accusations of neglect, turns to drugs and alcohol as a result, and eventually becomes the Man in the Woods, killing Sid as revenge for ruining his life, who is all alone at the honeysuckle bush far away from any witnesses since his lie scared them all away.

Western Animation

• In The Legend of Korra, there is Kuvira, who starts out as a harmless background character in season 3 who helps save Korra's father in the finale. However come the final season, she is put in charge of stabilizing the Earth Kingdom after the assassination of the queen, and her fascist methods of unifying the country put her at odds with the main characters.
• She-Ra and the Princesses of Power: Catra starts out as Adora's friend and general Anti-Villain, but her severe Inferiority Superiority Complex drives her mad as she gets constantly one-upped by She-Ra and abused by their step-mother Shadow Weaver. Eventually, Shadow Weaver defects, convincing Catra that the forces of evil would rather redeem themselves than admit Catra was worth something, which causes her to snap and try to use a superweapon that goes out of control and kills some very important people, leaving Adora devastated and utterly vengeful against Catra.^note Ironically, this put her in the best position to protect her people, as she had enough street cred from her super-villainy to convince Horde Prime to not destroy the giant superweapon (which happened to be the planet itself), or worse, accidentally activate it.
• In book 3 of Infinity Train, Simon is initially the deuteragonist and Grace's best friend, but as Grace begins to question the tenets of the Apex, their relationship begins to sour as he continues to insist that the teachings of the Apex are right even as evidence to the contrary begins to pile up. His status as a villain is cemented in episode 5 when he murders Tuba, and in the season finale he's become the dictator of the Apex and the final enemy Grace must overcome.
• Eddie Brock in The Spectacular Spider-Man starts out as Peter Parker's long-time best friend and a genuinely nice guy, only for a chain of events to lead him to become gradually more bitter toward both Spider-Man and Peter, culminating in his transformation into Venom.
• Dogs in Space: Kira demonstrated a great contempt for humanity since Garbage and his crew first encountered her. But following Garbage's near-sacrifice of his friends in what would have been a failed bid to save humanity, Kira takes advantage of his insecurities and desperation to atone to manipulate him towards her scheme of abandoning humanity to extinction in favor of finding a planet for dogs. Even if her plot could potentially end up killing the dogs she seeks to save, or permanently rob them of their sapience.
• Tangled: The Series:
  • The Arc Villain of Season 1 is Varian, who starts out as a charming ally to Rapunzel and her friends, but becomes an unstable, murderous villain after he suffers a personal tragedy that he blames Rapunzel and the kingdom of Corona for rather than take responsibility for it himself.
  • Season 2 has Cassandra. In the mid-season special, she reflects on how she has always felt left out and treated as unimportant by everyone around her. After Rapunzel accidentally severely burns her hand by using the Hurt Incantation, it's a slow downhill climb for Cass as she continues to feel left out and even learns the truth about her birth mother abandoning her as a child. It all culminates in the season finale, with her grabbing the Moonstone and becoming the Big Bad (sort of) of Season 3.
• Total Drama: In season 1 Courtney became more vindictive, competitive and unwilling to accept fault but happy to point it out in others as the series progressed. Then Harold rigged the votes to get her eliminated to get back at Duncan and she took it very badly. After that, while other contestants got over being eliminated, anytime we saw her she was either verbally or physically attacking someone, and when given another chance to get the money she wasted no time betraying and backstabbing any friend or acquaintance she'd made over the course of the season. When even after that she failed to get the money and wasn't even allowed to compete for it in the second season, she sued Chris to be allowed to compete again and get special treatment and quickly became the main antagonist of the season.

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