History Main / SuddenSequelHeelSyndrome

* ''VideoGame/PuyoPuyo7'' features the sudden introduction of a dark version of Arle as a villain, with Arle usually being a protagonist character throughout the ''Puyo Puyo'' series, including in the previous game, ''15th Anniversary''. Other characters wonder what happened to the real Arle; [[spoiler:Dark Arle actually ''is'' the real Arle, but under the possession of [[EldritchAbomination Ecolo]]]].

* Joker, the head of the British Library special forces in ''Anime/ReadOrDie''. Between the OVA, where he's on the side of the good guys, and R.O.D The TV, the death of Gentleman (the ManBehindTheMan of hundreds of years of British history who envisioned a sort of Utopia under the British Empire) shifts Joker into WellIntentionedExtremist territory, working toward what he sees as Gentleman's dream by means ranging from ethically dubious to outright evil.
* ''Anime/YuGiOh'' Season 4 turned Mai Valentine, the gang's CoolBigSis, into an angst-ridden member of a villainous biker gang. It turns out she was under MoreThanMindControl by the ArcVillain, Dartz.

* Season 3 of ''Literature/ShakuganNoShana'' [[spoiler:has the male protagonist, Yuji Sakai, of the first two seasons, suddenly becoming the BigBad, leaving the female lead and love interest Shana shocked and confused]].
* Played straight and zigzagged in ''Manga/TokyoGhoul''[=:Re=], which takes place after a two year TimeSkip:
** [[TheCutie Hinami]] Fueguchi was [[CorruptTheCutie enticed]] to join [[TheSyndicate Aogiri Tree]], through her desire to become stronger. She returns as a prominent member handling the group's intelligence network.
** PluckyComicRelief Seidou Takizawa turns out to be NotQuiteDead, and returns as an AxCrazy [[HalfHumanHybrid One-Eyed Ghoul]] serving as Aogiri's first successful SuperSoldier. He proceeds to slaughter his way through every Investigator he crosses paths with, taking the time to chat with a former pupil before tearing her head off because she used to talk during lectures.
** Played with, depending on [[GreyAndGrayMorality which side]] has the SympatheticPOV. Ken Kaneki returns as AmnesiacHero Haise Sasaki, working for the [[HunterOfMonsters CCG]] as a Ghoul Investigator and mentor to an experimental squad of SuperSoldiers. While he remains the protagonist, his former friends now have to worry about him hunting them down if they cross paths again.

* In ''Manga/TheSevenDeadlySins'', Arthur Pendragon and Jericho was steadfast allies of the country Liones and the heroes. In the sequel, ''Manga/FourKnightsOfTheApocalypse'', Arthur has turned into a paranoid and xenophobic king due to seeing the atrocities of nonhuman races and is determined to make Camelot survive, no matter what it takes or how many people he kills. He even declares war on Liones due to a prophecy saying four kids from there are destined to destroy him. Jericho defected to Arthur's side due to him promising a world where she could have Lancelot's love.

* ''ComicBook/FantasticFour:'' In Roy Thomas's run, the 50s hero Marvel Boy returns as The Crusader, apparently having gone insane since his home on Uranus was destroyed by mysterious causes, and is now on a RoaringRampageOfRevenge against some bankers he holds as partially responsible. A few decades later this was retconned as being an insane, defective clone of Marvel Boy the Uranians cooked up. The real Marvel Boy's just fine and dandy.
* Jean Loring in ''ComicBook/IdentityCrisis2004'', who went completely off her rocker to try winning back the affection of her ex-husband, [[ComicBook/TheAtom Ray Palmer]].

* ComicBook/{{Supergirl}}: Post-Crisis Linda Danvers retired from superheroics after ''Comicbook/ManyHappyReturns'', but returned in ''ComicBook/{{Shadowpact}}'', transformed into a vengeful "Fallen Angel".
* ComicBook/{{Batgirl 2000}}: Cassandra Cain during DC's ''One Year Later'' storyarc. This was not a popular storyline (she was quite OutOfCharacter even ''aside'' from the evil) and eventually got {{Ret Con}}ned into mind control.

* In ComicBook/WorldWarHulk we learn that Miek, who was a friend and ally of Hulk in ''ComicBook/PlanetHulk'', was the one who let the explosion destroy Sakaar just so Hulk would reach [[UnstoppableRage the WorldBreaker stage]]. This was at least was foreshadowed by him passing a DespairEventHorizon at the apparent extinction of his species, leaving him the only one of the Warbound without a happy ending.
* In ''ComicBook/TheUltimates 2'', Black Widow is revealed to be TheMole working for the Liberators and her native country, Russia.

* In ''Fanfic/HalfLifeFullLifeConsequences'', Gordon Freeman, TheHero from canon and the protagonist's heroic brother in this fanfic, comes BackFromTheDead in "What Has to Be Done", as a "zombie goast" who wants to kill his brother out of revenge, [[spoiler:and again as a BrainwashedAndCrazy slave of the Combines in "Free Man", although once he's defeated, he [[DyingAsYourself dies as himself]].]]

* ''Film/StarTrekVITheUndiscoveredCountry'' turns Admiral Cartwight from ''Film/{{Star Trek IV|The Voyage Home}}'' into a co-conspirator with the bad guys.
* ''Film/MissionImpossible1996'' turns Jim Phelps, the unwavering mastermind of [[Series/MissionImpossible the original series]], into a bitter cynic who betrays his team for a multi-million-dollar payoff. To say that fans of the series were angry would be an understatement. Greg Morris, who played Barney Collier in the original, walked out of the movie in disgust, while Creator/PeterGraves and Creator/MartinLandau also voiced their displeasure (Graves turned down an offer to reprise his role as Phelps because of this).
* Ugg the alien bounty hunter who was one of the heroes in the first three ''Film/{{Critters}}'' film is the main villain in the fourth film.
* ''Film/TerminatorGenisys'': [[spoiler:John Connor is [[ReforgedIntoAMinion turned into a Terminator]] and sent back in time after Sarah and Kyle]].
* ''Film/CaptainAmericaTheWinterSoldier'':
** The film reveals that the eponymous Winter Soldier is Cap's old war buddy Bucky Barnes, now BrainwashedAndCrazy. Luckily, he's redeemed at the end.
** It also does this to many SHIELD agents who had appeared throughout the [=MCU=]'s existence who were revealed to be [[spoiler:Hydra moles]], including Jasper Sitwell and Senator Stern.
* Although neither side was ever shown to be completely in the right or wrong (being a Captain America movie, we can assume that Team Cap were the "heroes" and Team Iron Man the "villains"), the two sides of ''Film/CaptainAmericaCivilWar'' rapidly approach lethal measures in the airport fight, culminating in a shot meant for Falcon from Vision's Mind Stone instead hitting War Machine's Arc Reactor, cutting off the suit's power and paralyzing him from the waist down in the resulting crash. Despite this, Iron Man still relents upon finding Cap and Bucky in Siberia, until Zemo reveals that the Winter Soldier killed Stark's parents, launching Iron Man into a rage-fueled, NoHoldsBarredBeatdown on the pair.
* Koba in ''Film/RiseOfThePlanetOfTheApes'' wasn't the nicest ape, but he still had justification for the things he did and supported Caesar. In ''Film/DawnOfThePlanetOfTheApes'', he becomes the BigBad as his hatred of the humans becomes so great that [[FalseFlagOperation he attempts to assassinate Caesar and sets fire to their camp and blames the humans to start a war against them]].
* ''Film/JurassicWorld'', Henry Wu is a MorallyAmbiguousDoctorate who strikes a deal with the BigBad to explore the possibility of weaponizing dinosaurs. He [[spoiler: deliberately engineers the I. Rex to be strong and smart enough that it will inevitably escape, even though this would endanger everyone on the island (implied to be thousands of people when it happens) and destroy any future the park might have had as a business]]. Harboring no loyalty towards Masrani (his boss) or the dream of the late John Hammond, his sole motivation in the film seems to be ForScience. This is rather jarring when compared to his appearance in the first movie, where he never showed any antagonism towards the other characters or malevolent intent in creating dinosaurs (though admittedly, he was a pretty minor character). He grows to regret his actions by the time of ''Film/JurassicWorldDominion'', managing to redeem himself in the end.
* ''Film/PacificRimUprising'' has [[spoiler: Newt become the BigBad after his repeated drifting with a Kaiju Brain allows the Precursors to [[BrainwashedAndCrazy get inside his head]].]]
* In ''Film/TransformersTheLastKnight'', William Lennox, one of the Autobots' human allies in the original trilogy, has reluctantly been forced to join the TRF, a task force designed specifically to hunt both Autobots and Decepticons alike.

* In the first story of G.K. Chesterton's ''Literature/FatherBrown'' series, detective Aristide Valentin of the Paris police force is a likable InspectorLestrade to the title character, totally fooled by Father Brown's ObfuscatingStupidity but competent enough to follow the trail of clues the little priest leaves for him. In the next story, [[CharacterDerailment however]], he becomes a StrawAtheist who murders a man to prevent him from leaving money to the church in his will. (And, for extra irony points, the villain from the first story is subsequently given a HeelFaithTurn to become TheWatson.)
* In ''Literature/InheritanceCycle,'' [[EnsembleDarkhorse Murtagh]] initially looks like he ran afoul of SuddenSequelDeathSyndrome with NoBodyLeftBehind from an ambush at the start of the second book, but appears at the end alive...and now ForcedIntoEvil and another DragonRider because he was actually captured and brought back to [[BigBad Galbatorix]], who tortured him and used [[IKnowYourTrueName his true name]] to bind him to his will. With that said, Murtagh goes for BotheringByTheBook and resisting where he can, refusing to take Eragon captive after curbstomping him, merely taking his father's sword back. Galbatorix, however, gets wise to this and mind-controls Murtagh for special messages. [[spoiler:In the last book, Galbatorix torturing Nasuada allows Murtagh to change his true name and gain his freedom]].

* Atticus Finch, an iconic hero in ''Literature/ToKillAMockingbird'', becomes a senile old racist in its sequel, ''Literature/GoSetAWatchman'' (written first but published and set afterwards). This is shocking both in and out of universe, with Jean-Louise expressing her distaste, and many critics have also voiced displeasure at the dismantling of one of the most inspiring heroes in American history.

%%* Sikozu in ''Series/{{Farscape}}: The Peacekeeper Wars.''
* In ''Film/KamenRiderXSuperSentaiSuperheroTaisen'', former [[Series/KaizokuSentaiGokaiger Gokai Red]] Marvelous actually takes command of a LegionOfDoom to further his quest for the Greatest Treasure. [[spoiler: All a plan between the Super Sentai and the Kamen Riders to manipulate the bad guys, of course]].
** ''All'' the Gokaigers in the usual teamup with Go-Busters. Naturally, they were also faking it.
* During the original run of ''Series/DoctorWho'', Chancellor Borusa had in the past been depicted as a politically motivated member of the Time Lords High Council, but ultimately someone whom the Doctor could work with and even regard as a friend. In "[[Recap/DoctorWho20thASTheFiveDoctors The Five Doctors]]", he turned out to be the villain, orchestrating a mad scheme to resurrect Rassilon and gain immortality.
** Admittedly, every time the show returned to Gallifrey, it seemed that more of the cracks in the Time Lords' "perfect society" would show, to the point where the Doctor would call them out, declaring them, "the oldest civilization, decadent, degenerate and rotten to the core!" By the time of the new series, the entire Time Lords species had crossed a collective MoralEventHorizon, plotting to destroy all of time to preserve themselves. This ended up being retconned, however, as the actions of a small minority of Time Lords, after which they save the Doctor's life by granting him a new regeneration cycle.

* ''{{Series/Angel}}'':
** There were plans were to bring (good guy) Doyle back as an antagonist in Season 5, but Glenn Quinn's death put a stop to those. This was changed to bringing back Lindsey to fulfill the role. While Lindsey had originally been an antagonist, by the time he left in Season 2, he'd morphed into more of an AntiHero who had buried the hatchet with Angel and moved on from working with the villains. Much like it would have done with Doyle, Season 5 returned him in an antagonist role.
** The demon Skip was a seemingly benevolent entity or GoodIsNotNice persona in his first two Season 3 appearances. Then it turns out he was working for the BigBad Jasmine the whole time when he shows up in Season 4.

* In ''VideoGame/MetalGear'':
** Gray Fox, Schneider and Dr. Pettrovich were originally on Solid Snake's side in the first game, ''VideoGame/MetalGear1''. In ''VideoGame/MetalGear2SolidSnake'', all three defected to Zanzibarland for different reasons.
** ''VideoGame/MetalGearSolid2SonsOfLiberty'' cheerfully subverts this -- the villain claims to be Solid Snake, but he clearly isn't.
** Zero, Para-Medic and Sigint, Naked Snake's support crew from ''VideoGame/MetalGearSolid3SnakeEater'', are revealed to be the founding members of The Patriots (the shadowy organization behind the events of ''VideoGame/MetalGearSolid'' and ''VideoGame/MetalGearSolid2SonsOfLiberty'') in ''VideoGame/MetalGearSolid4GunsOfThePatriots''. While in retrospect it can be argued that ''Metal Gear Solid 3'' was already setting them up as the future founders of the Patriots, as there were hints of what they would become throughout their interactions with Snake, their nice personalities in the game made them very unlikely they would ever go dark.
** Dr. "Huey" Emmerich in ''VideoGame/MetalGearSolidPeaceWalker'' was a meek scientist (much like his son Hal) who gets easily intimidated by the game's antagonist, Hot Coldman, and is too shy to confess his love to Dr. Strangelove, who is portrayed as a totally harmless character. In ''VideoGame/MetalGearSolidV'', he allegedly sells out MSF to XOF, the Cipher Strike Force responsible for the destruction of Mother Base during the events of ''Ground Zeroes'', seemingly kills his wife Strangelove by locking her inside the A.I. Pod and leaving her to starve to death, spreads the Parasite outbreak and helps Eli hijack Sahelanthropus in ''The Phantom Pain''. Granted, we never actually see Huey commit any of these hideous deeds on-screen, but his ever-changing narrative every time he is interrogated over accusations doesn't give him much credibility.
* In the 2009 ''VideoGame/BionicCommando'' game, the BigBad is revealed to be [[spoiler:Super Joe, the war hero you rescued in the original ''Bionic Commando'']].
* ''VideoGame/FinalFantasyX2'' inverts it. Tromell Guado was TheDragon to Seymour, actively sending people out to kill the protagonists after they murdered Seymour, along with destroying the evidence that Seymour killed his own father. In the two-year TimeSkip the entire Guado race suffered a collective MyGodWhatHaveIDone -- and exiled themselves to the Macalania Woods. One sidequest is preventing the Ronso from slaughtering the tribe. If the player does things correctly [[spoiler:Tromell will become the new leader of the Guado and direct them towards a brighter future]].

* Lloyd Irving in ''VideoGame/TalesOfSymphoniaDawnOfTheNewWorld''. Well, sort of. [[spoiler:It was an impostor and the real Lloyd was only hindering your goals because he was trying to set things right as well.]]
* ''VideoGame/WingCommander'':
** ''[[VideoGame/WingCommanderTheKilrathiSaga Wing Commander III: Heart of the Tiger]]'' has [[spoiler:Col. Ralgha nar "Hobbes" Hhallas, who was throughout game ''II'' a ProudWarriorRaceGuy who was disgusted with his race's lack of honor, suddenly do a FaceHeelTurn in which he turns out to have been a sleeper agent hiding behind a fabricated personality]].
** Likewise, the BigBad of ''VideoGame/WingCommanderIVThePriceOfFreedom'' [[spoiler:turns out to be Admiral Tolwyn, who lost his direction in life and ultimately went rather nuts once he no longer had a war to fight. Although he was something of a jerk towards your maverick ace character throughout the series, he was also mostly the main BigGood]].

* ''VideoGame/SoulSeries'':
** This happens to heroine-turned-ActionMom, Sophitia Alexandra, in ''Soulcalibur IV''; where she's made to defend [[ArtifactOfDoom Soul]] [[EvilWeapon Edge]] in order to save her daughter's life. What's worse, Sophitia begins SlowlySlippingIntoEvil because EvilFeelsGood, making her even more somber and conflicted. [[BreakTheCutie The entire]] [[TrappedInVillainy ordeal]] brings her dangerously close to the DespairEventHorizon.
** The same game reveals that that eponymous Soul Calibur itself is a KnightTemplar at best and EvilAllAlong at worst. When the sword reaches full power and gains sentience, it's shown that Soul Calibur, long thought to be the "good" sword throughout the series, [[UnholyHolySword is technically just as "evil" as its counterpart]]. [[BothOrderAndChaosAreDangerous The difference]] is that the Soul Edge likes to spread chaos and misery while Soul Calibur [[WorldOfSilence wants tranquility, order and peace... by freezing the entire world solid]]. [[VideoGame/SoulcaliburV The next game]] ups the ante by having the spirit of Soul Calibur, Elysium, pull a DeadPersonImpersonation on Sophitia ([[BusCrash who died between games]], saving Pyrrha with the Soul Edge shard embedded near her heart from the events of ''Soul Edge'' at the cost of her own life) in order to manipulate her vengeful son Patroklos, leading him to [[spoiler:''kill'' his own sister Pyrrha after she's become malfested (fortunately, there's a ResetButton courtesy of Edge Master)]] and later trying to outright take control of Pat via a BattleInTheCenterOfTheMind, with the implication she'll turn him into Soul Calibur's equivalent of Nightmare if she wins. The series did hint at this development a few times prior [[note]]Inferno's ending in ''Calibur'' has Soul Edge deliberately corrupt Soul Calibur and transform it into a new cursed sword; ''Soulcalibur II'' features an ambiguously canon/WhatIf version of the spirit sword known as Soul Calibur (Evil), presumably depicting either the aforementioned ''SCI'' ending and/or the aftermath of Soul Calibur being trapped in Astral Chaos with Soul Edge during the four-year period between ''SCI'' and ''SCII''; and backstory materials surrounding Algol (the man responsible for Soul Calibur's creation via purified Soul Edge shards who appears as the FinalBoss of ''IV'') note that his restless spirit inadvertently corrupted the holy sword when he sacrificed his life to create it[[/note]], but for many the twist was both unexpected and very poorly done.

* ''VideoGame/ContraShatteredSoldier'' reveals that the Blood Falcon Commander is none other than Lance Bean, Bill Rizer's partner from earlier games. [[WellIntentionedExtremist He went insane]] trying to reveal the GovernmentConspiracy he and Bill were duped into helping cover up. Likewise, in ''VideoGame/NeoContra'', [[spoiler:Lucia, Player 2 in ''Shattered Soldier'']] is revealed to be part of the QuirkyMiniBossSquad and dies attempting to kill Bill and exterminate humanity for reasons which are not even vaguely explained.
* Alex Mercer becomes the BigBad in ''VideoGame/Prototype2'' after crossing the DespairEventHorizon.
* ''VideoGame/WorldOfWarcraft'' has gone ''hard'' on various characters from the [[VideoGame/{{Warcraft}} previous games]] or the [[Franchise/WarcraftExpandedUniverse expanded universe]] in order to turn them into bosses which may be killed for loot. "Going mad," is apparently an occupational hazard for lore characters, as it's the most common excuse used to turn them into raid bosses. This list includes Illidan Stormrage, Kael'Thas Sunstrider, Malygos, Norzdormu, Fandral Staghelm, and Archbishop Benedictus.
** Illidan is a notorious example, to the point where Blizzard vowed to one day bring him back and redeem him to make up for it. They even admitted that they only made him a villain so the expansion would have a popular character to confront and get loot from. In ''VideoGame/{{Warcraft}} III'', Illidan was a complex NominalHero who used any means necessary to gain power and save his people, in that order, but despite fears from those around him never succumbed to the corruption of the dark powers he was toying with. Come the ''Burning Crusade'' expansion, he's been "driven mad" and turned to evil with no adequately satisfying explanation. They finally followed through in the ''Legion'' expansion, making him one of the major allies (though calling him "[[WildCard hero]]" would still be a stretch) and revealing his "driven mad" motivations was more him [[PoorCommunicationKills refusing to explain the reasonings behind his actions to anyone save his closest allies, which made people rather obviously think he was crazy/evil]] (something he had technically suffered from as early as ''Warcraft III'').
** Blizzard also expressed regret over Kael'thas's characterization, but after almost immediately bringing him back from the dead as an even more desperate Legion pawn, figured they missed their chance to properly repair his character.
** Malygos the Spell-weaver was introduced in the books as the Aspect of the Blue Dragonflight and protector of all magic in Azeroth, a friendly and wise dragon, who was only brought down when Deathwing wiped out most of the blues 10,000 years ago. Malygos then participated in the defeat of Deathwing in modern times, and the blues are shown as slowly coming back from the brink. Then he inexplicably decides to wipe out all mortal magic-users and becomes a bad guy, forcing Alextrasza the Life-binder to help put him down. The official line is that Malygos ''wasn't'' crazy, however, but rather doing his job properly for the first time in thousands of years. However, this rather jars with his attempts to police mortal mages being more dangerous than the magic itself.
** The Zandalari trolls were introduced as peaceful and neutral to Horde and Alliance alike, seeking to stop the return of Hakkar and record the history of the collapsing Drakkari troll empire. In ''Cataclysm'' they began inciting the Amani and Gurubashi to reclaim their empires due to growing fears about trolls being wiped out. ''Mists of Pandaria'' escalated this when the Zandalari willingly joined forces with [[LawfulEvil the Thunder King]]. Here their reason is finally explained: [[DrivenToVillainy The Cataclysm is causing their homeland to sink into the ocean; without a new homeland they'll be wiped out]]. Come ''Battle for Azeroth'', the Horde story campaign revolves around allying with them, eventually making them a playable faction after cleaning up the corrupt factions that caused the war in the first place.
** This happens to the Horde leaders, most notably Garrosh and Sylvanas. For Garrosh, he was turned into a villain after he received very poor player feedback for being overly aggressive and receiving empty hype, replacing the very popular Thrall in the process. This ended with a civil war where Horde players had to invade their own capital city. The problem with Sylvanas, on the other hand, is more annoyance that ''another'' Horde warchief turned into a major villain rather than it seeming out of character for her to be so vicious.
* The AxCrazy BigBad of ''VideoGame/ArmyOfTwo 3: The Devil's Cartel'' is revealed to be [[spoiler: Salem, one of the two main characters from the first two games.]]
* In ''VideoGame/FireEmblemShadowDragonAndTheBladeOfLight'', Hardin is on the hero's side. In ''VideoGame/FireEmblemMysteryOfTheEmblem'''s second book, it is revealed that he has turned evil. [[spoiler:This is due to the BigBad of the first game corrupting him with an ArtifactOfDoom, which exploited Hardin's insecurities over not being loved by Nyna, whose marriage to him was purely political.]]

* ''Franchise/DeadRising'':
** ''VideoGame/DeadRising3'' brings back [[spoiler:Isabella Keyes]] as a WellIntentionedExtremist behind all of the events of that game. In a lesser example, [[spoiler:Chuck Greene]] becomes a crime boss [[spoiler:to provide his daughter Katey with more Zombrex. This drove away his love interest|s Stacey from [[VideoGame/DeadRising2 the previous game]] and Katey, who took on the name "Annie" and ran away from home]].
** In the AlternateContinuity of ''VideoGame/DeadRising2OffTheRecord'', [[spoiler:Chuck Greene]] goes crazy and becomes a psychopath after [[spoiler:Katey]] dies.

* Though calling [[Franchise/ResidentEvil Ada Wong]] a "good" guy [[WildCard is being rather generous]], she was never as outright heinously evil as she is in ''VideoGame/ResidentEvil6'' where she mercilessly infects the same soldiers who protected and escorted her to safety [[ForTheEvulz just for kicks]] and is soon discovered to be the leader of a [[NebulousEvilOrganization NEO Umbrella]] that plans to [[TheEndOfTheWorldAsWeKnowIt destroy the world]]. [[spoiler:It's revealed that Ada is actually [[EvilTwin a woman named Carla Radames]] who has been subjected to CloneByConversion thanks to the [[LoveMakesYouCrazy Ada-obsessed]] BigBad behind Neo Umbrella. The ''real'' Ada is still the same [[DeadpanSnarker snarky]], {{pragmatic|villainy}} AntiVillain she always was and is actively working to stop Carla.]]
* ''VideoGame/KnightsOfTheOldRepublic'':
** In the first ''Knights of the Old Republic'', Master Vrook is a character who many players saw as a grumpy, grouchy old man. In truth, he only acts this way if the player takes dark side options. If they play light side and talk to Vrook, he'll compliment them on their actions. By the time of [[VideoGame/KnightsOfTheOldRepublicIITheSithLords the sequel]] however, {{Flanderization}} sets in and he just hates you regardless of how well you act.
** By the time of ''VideoGame/StarWarsTheOldRepublic'', Revan, the protagonist of the first game, has clearly gone insane from his 300 years of captivity. At first, he takes over an old battle station and cooks up a plan to [[OmnicidalManiac wipe out 98% of the Imperial population]] (and likely, a good chunk of the Republic's population in the process). Then he returns, waging war on both the Republic and the Empire as the leader of a fanatical cult. [[spoiler:Then it turns out that this is only ''half'' of Revan, who had become [[LiteralSplitPersonality split]] between his good side and his dark side, with the latter becoming the antagonist cult leader.]]
* A minor example in ''VideoGame/FarCry4''. CIA agent Willis Huntley, a major character around the mid-point of [[VideoGame/FarCry3 the previous game]], shows up again to give new protagonist Ajay a couple missions. These missions turn out to be [[spoiler:eliminating other CIA assets in the area to remove evidence of the CIA's presence in Kyrat, after which he throws Ajay out of his plane, leaving him to be captured by the guards of the person whose lieutenants (the aforementioned other CIA assets) he just killed.]]
* In ''VideoGame/TimeCrisis'', Robert Baxter was one of the player characters in the second game. [[spoiler: Then in the fifth, he becomes the BigBad.]]
* ''VideoGame/DawnOfWar 2: Chaos Rising'' introduces the Chaos faction, as well as a KarmaMeter that determines which of your characters is slowly falling to Chaos. [[spoiler:In-game, the traitor will wind up being the Sergeant with the most Corruption points by the time you've attacked the Honour Guard stronghold just before the mission to go after them. If you keep everyone pure till then, the traitor will be [[MissionControl Techmarine Martellus]] instead. However, the sequel ''Retribution'' establishes that canonically Devastator Sergeant Avitus turns traitor.]]
* ''Franchise/TheElderScrolls'':
** Hermaeus Mora, Daedric Prince of [[KeeperOfForbiddenKnowledge Knowledge]], in ''[[VideoGame/TheElderScrollsVSkyrim Skyrim]]''[='s=] ''Dragonborn'' DLC. In previous appearances, including vanilla ''Skyrim'', Mora is always a neutral entity, though he could be a bit ruthless in achieving his goals. In ''Dragonborn'', he [[TheChessmaster orchestrates everything that happens]], putting millions of innocent lives at risk, just to obtain the "secrets" of the [[NobleSavage Skaal]].
** In a case of sudden ''prequel'' heel syndrome, Sheogorath, the Daedric Prince of [[MadGod Madness]], is ''much'' more malevolent and sinister than he ever was before in ''VideoGame/TheElderScrollsOnline''[='s=] Mages Guild arc.
** To sum it up, whenever Aedra and Daedra are involved, expect BlueAndOrangeMorality to be in full effect. Almalexia, supposedly a benign entity, and Azura, a Daedric Prince, are the greatest examples, and even those may shift depending on the time period and stakes at play.
* ''Franchise/MassEffect'':
** While Donnel Udina is never a ''[[CorruptPolitician likable]]'' character, he is at least consistently presented as an advocate for humanity, and receives several PetTheDog moments in ''VideoGame/MassEffect3'' after the invasion of Earth, which makes it all the more surprising when [[spoiler: he turns out to be TheMole for Cerberus and helps with the attempted coup on the Citadel]], although it's implied he did so out of desperation following the invasion.
** The Illusive Man is the founder of the NGOSuperpower Cerberus that performs all manner of mad science experiments to ensure humanity's survival. While Cerberus was presented as villains in the first game through their unethical experiments, in the second they bring Shepard BackFromTheDead and prove themselves to be [[WellIntentionedExtremist Well-Intentioned Extremists]] by explaining their previous actions and doing everything they can to help him/her stop the Reapers. However by the third game, [[spoiler:[[JumpingOffTheSlipperySlope they turn into full-blown villains]] due to the Illusive Man's indoctrination by the Reapers and perform actions such as killing civilians, attempting to provoke a war between the Turians and Krogan, attacking the Citadel, hunting down former members, and turning people into Husks]].
* Inverted in ''VideoGame/UnchartedTheLostLegacy''. During ''VideoGame/Uncharted4AThiefsEnd'', Nadine Ross is TheDragon and an enemy of Nate. In ''The Lost Legacy'', she retires from the PMC business and takes up treasure hunting as TheLancer to Chloe Frazer. While she's still bitter about the events of the games due to the hand the Drake Brothers had in dismantling her organization and angered that Chloe was working with Sam, she ultimately buries the hatchet with him by game's end.
* ''VideoGame/{{Torchlight}}'': The Alchemist was one of the player characters classes in the first game, but by the time of the sequel, his experiments with the [[TheCorruption the Heart of Ordrak]] have turned him into the BigBad.
* ''VideoGame/PuyoPuyo7'' features the sudden introduction of a dark version of Arle as a villain, with Arle usually being a protagonist character throughout the ''Puyo Puyo'' series, including in the previous game, ''15th Anniversary''. Other characters wonder what happened to the real Arle; [[spoiler:Dark Arle actually ''is'' the real Arle, but under the possession of [[EldritchAbomination Ecolo]]]].
* A rare inversion of this trope occurs in ''VideoGame/NEOTheWorldEndsWithYou'': whereas in the original game Sho Minamimoto is a powerful Reaper who causes much havoc and even gives the heroes trouble before he goes down, in the First Week of this game he's [[spoiler:supposedly]] a Player working alongside Rindo and Fret as part of the Wicked Twisters. [[spoiler:However, it's eventually revealed that he only assisted the Wicked Twisters throughout the First Week as a means to determine the negative side-effects of Rindo's Rewind powers, and he is fought at Day 4 of the Final Week, prompting Neku to appear and save the day. At the Final Day, though, he assists the heroes and the Shibuya Reapers into containing the Plague Noise.]]
* ''VideoGame/MegaManZero'' begins with the titular Zero being awakened after a century of stasis and being told that X is the leader of Neo Arcadia, and has been systematically been retiring reploids under false pretenses of them having gone Maverick. [[spoiler: It's later revealed that this X is a copy created by Ciel to run Neo Arcadia, but who lacked X's moral judgments (and presumably Dr. Light's safeguards) and grew to consider all reploids a threat to humans. The original X no longer has a body and now exists as a Cyber Elf who has been guiding Zero the entire time.]]
* ''VideoGame/GalaxyAngelII'': The first installment, Zettai Ryouiki no Tobira, has Forte Stollen, former leader of the original Moon Angel Wing from ''VideoGame/GalaxyAngel'', joining up with rebel forces to take over Planet Seldar, allegedly because they're taking too long to integrate the EDEN technology into their culture. [[spoiler:Halfway through the game, it's revealed that Forte had been blackmailed by Verel into leading the coup by holding Milfeulle and the Seldar royal family hostage. She does her best to try and minimize the casualties and, once she's finally able to escape, turns herself in to be judged by her actions]].
* Alvis in ''[[VideoGame/XenobladeChronicles1 Xenoblade Chronicles]]'' is a mysterious and cryptic individual who ultimately sides with Shulk and helps him defeat the [[GodIsEvil Evil God]] who had been planning to destroy and recreate the world of Bionis. Much later, in ''VideoGame/XenobladeChronicles3FutureRedeemed'', Alvis is revealed to have become an enemy to both Shulk and Rex, the protagonist of ''VideoGame/XenobladeChronicles2''. [[spoiler:It's actually a bit more complicated: As the personification of a microprocessor called Ontos, Alvis lost the ability to feel empathy and make nuanced decisions after the loss of its counterparts Pneuma and Logos--all of whom are meant to balance each other out--and ended up splitting into two beings: Alpha, the cold and logical figure that has Alvis' appearance and whom wants to destroy Aionios and create a new world; and A, who has Alvis' memories and empathy, and thus has sided with the Heroes once more.]]
* Chronologically, when ''VideoGame/{{Tekken}} 2'' was released, the shock value was that the FinalBoss was the first game's protagonist, Kazuya Mishima, while the main focus is the first game's FinalBoss, Heihachi Mishima. Kazuya was originally depicted as cookie-cutter as possible in the first game, but by the second game, he's all on board of committing atrocities with a glee. Latter games would later reveal that this was an inevitable outcome: Kazuya has walked the path of villainy even before the first game began, he was just pretty good at hiding it until he reached his initial goal of deposing Heihachi. Ever since then, when ''Tekken'' fans see Kazuya returning and acting villainous, no one is surprised anymore.
* ''VideoGame/{{Marathon}}'': In the first game, Tycho (the third A.I. aboard the ''Marathon'') is antagonistic to Durandal on the behalf of humans. Come the sequel and one painful reconstruction[=/=]torture by the Pfhor later, and he is firmly in camp evil. This effectively makes Tycho and Durandal's roles switch in the sequels. While Durandal is working for his own goals they generally will line up with the players, while any time you're working under Tycho it is under duress.
* ''VideoGame/CriminalCase'': [[spoiler:Dr. Ernest Emerson and Dr. Shweta Noorani]] appear as minor one-shot characters in ''VideoGame/CriminalCaseWorldEdition'' where they end up being innocent of killing the VictimOfTheWeek, before returning as major antagonists in the sequel, ''VideoGame/CriminalCaseTheConspiracy'', with [[spoiler:Ernest]] being an ArcVillain and [[spoiler:Shweta]] TheDragon.
* Subverted in ''VideoGame/TheLegendOfZeldaTearsOfTheKingdom'' where [[spoiler:Yunobo has seemingly turned into a CorruptCorporateExecutive and the fantasy equivalent of a drug lord, but it becomes obvious very quickly that he's being brainwashed (to the point that his {{Boss Subtitle|s}} is "Clearly Not Himself"). Once the mask controlling him has been destroyed, he goes right back to being his old lovable self (though a good deal braver than he was in ''Breath of the Wild'').]]

* ''VideoGame/{{Marathon}}'': In the first game, Tycho (the third A.I. aboard the ''Marathon'') is antagonistic to Durandal on the behalf of humans. Come the sequel and one painful reconstruction[=/=]torture by the Pfhor later, and he is firmly in camp evil.

* Talia Al Ghul in ''WesternAnimation/SonOfBatman'' was shown to be a very caring mother to Damien enough that she left him with Bruce after Deathstroke near killed everyone in the League of Shadows. However when she returns in ''WesternAnimation/BatmanBadBlood'', she has suddenly gone evil, tries to brainwash Batman into following her plans, and has no scruples about trying to kill her son. Even making a clone of him, aged him up and then ''killing him'' when he gets too clingy.

* The survivors of doomed worlds from ''ComicBook/CrisisOnInfiniteEarths'' (Earth-Two Superman, Superboy-Prime and Alexander Luthor Jr.) were brought back as the villains of ''ComicBook/InfiniteCrisis'', becoming contemptuous of UsefulNotes/{{the Modern Age|of Comic Books}} Franchise/DCUniverse and launching a scheme to forcefully return things to UsefulNotes/{{the Silver Age|of Comic Books}} status quo.

* Subverted in ''VideoGame/TheLegendOfZeldaTearsOfTheKingdom'' where [[spoiler:Yunobo has seemingly turned into a CorruptCorporateExecutive and the fantasy equivalent of a drug lord, but it becomes obvious very quickly that he's being brainwashed (to the point that his BossSubtitle is "Clearly Not Himself"). Once the mask controlling him has been destroyed, he goes right back to being his old lovable self (though a good deal braver than he was in ''Breath of the Wild'').]]

* In ''Webcomic/{{Homestuck}}'', the Alpha human kids ended the comic on the side of good. Starting from ''Literature/TheHomestuckEpilogues'' and carrying into ''Webcomic/Homestuck2'', [[spoiler:Jane becomes a xenophobic, sexually abusive warmonger and Dirk attempts to literally usurp the narrative by force.]]

* In ''Film/TheBabysitter2017'', Melanie os Cole's 12-year-old neighbor and his only friend at school. She even lets him take refuge at her dad's house so he can hide from Bee and her cult. However, by the start of ''Film/TheBabysitterKillerQueen'', Melanie has joined the cultists as their ''[[BigBadFriend new leader]]'' and plots to kill her former friend, without remorse.

** Also inverted for Wrestling/BobbyRoode, who started his WWE career in NXT as a heel, but turned face when he debuted on ''[=SmackDown=] Live'' in August 2017.

* ''VideoGame/{{Contra}}: Shattered Soldier'' reveals that the Blood Falcon Commander is none other than Lance Bean, Bill Rizer's partner from earlier games. [[WellIntentionedExtremist He went insane]] trying to reveal the GovernmentConspiracy he and Bill were duped into helping cover up. Likewise, in ''Neo Contra'', [[spoiler:Lucia, Player 2 in ''Shattered Soldier'']] is revealed to be part of the QuirkyMiniBossSquad and dies attempting to kill Bill and exterminate humanity for reasons which are not even vaguely explained.

* Maxwell Lord had always been depicted as a somewhat egotistical businessman who recreated the Justice League in part to make himself look good but ultimately proved to be a fairly honorable person. Then came ''ComicBook/InfiniteCrisis'', in which he turns out he originally founded the new League in order to undermine all superheroes. And, while originally, the reveal was that he was ''always'' evil, despite readers having seen his inner thoughts at multiple points in that Justice League run to prove otherwise, it was later expanded on him having family members negatively affted by superheroes that made him want to undermine, or at least monitor them.

* [[spoiler:Penelope Mouse]] from ''VideoGame/SlyCooper'' turns bum at some point between the [[VideoGame/Sly3HonorAmongThieves third]] and [[VideoGame/SlyCooperThievesInTime fourth]] game, [[AssPull and it came right the hell out of nowhere]].

* ''Film/TheBabysitterKillerQueen'': In the original ''Babysitter'' film (2017), Melanie was Cole's 12 year old neighbor and his only friend at school. She even let him take refuge at her dad's house, so he could hide from Bee and her cult. But by the start of the sequel, Melanie has joined the cultists as their ''[[BigBadFriend new leader]]'' and plots to kill her former friend, without remorse.
* ''Film/RoboCop2'': In the original ''Film/RoboCop1987'', the CEO of Omni Consumer Products is largely uninvolved in the story. In the sequel, he takes center stage as the CorruptCorporateExecutive driving the villainous plot.

* ''Film/{{Star Trek VI|The Undiscovered Country}}'' turns Admiral Cartwight from ''Film/{{Star Trek IV|The Voyage Home}}'' into a co-conspirator with the bad guys.
* The first ''Film/MissionImpossible'' film turns Jim Phelps, the unwavering mastermind of the original series, into a bitter cynic who betrays his team for a multi-million dollar payoff. To say that fans of [[Series/MissionImpossible the original series]] were angry would be an understatement. Greg Morris, who played Barney Collier in the original, walked out of the movie in disgust, while Creator/PeterGraves and Creator/MartinLandau also voiced their displeasure (Graves turned down an offer to reprise his role as Phelps because of this).

* ''Film/CaptainAmericaTheWinterSoldier''

** It also does this to many [=SHIELD=] agents who had appeared throughout the [=MCU=]'s existence who were revealed to be [[spoiler:Hydra moles]], including Jasper Sitwell and Senator Stern.

* Jean Loring in ''ComicBook/IdentityCrisis'', who went completely off her rocker to try winning back the affection of her ex-husband, [[ComicBook/TheAtom Ray Palmer]].