->''[[Series/{{Firefly}} Curse your sudden but inevitable betrayal!"]]''

* [[spoiler: Londo Mollari]] begins the ''Series/BabylonFive'' MythArc as the human commander's closest ally, but effectively becomes TheDragon as the series progresses. In fact, he [[FaceHeelRevolvingDoor vacillates between good and evil repeatedly]] as the series goes on.
** Also Talia Winters, once her (utterly psychotic) "sleeper" personality was unlocked.
** [[spoiler:...and Garibaldi in season 4, ]]due to a bad case of MoreThanMindControl.
** [[spoiler: ...and Anna Sheridan, ]]who could be assumed to be a good person prior to getting Shadowed.
* The third season of ''Series/{{Degrassi}}'' revolves entirely around Manny and Sean turning {{heel}}, then slowly turning back to {{face}}.
* Half the cast of ''Series/{{Alias}}''. Double-agency was a big part of the premise of the show, so it is to be expected.
** Perhaps most notable was [[spoiler:Lauren, Vaughn's (first) wife]], which was probably supposed to be a big surprise, but which everyone saw coming anyway.
** There were several in-show Face-Heel Turns that the audience was in on before the characters were:
*** [[spoiler:Sydney was a double-agent for the real CIA, supposedly working for SD-6, and when she revealed herself to Dixon,]] he saw that as a face-heel turn. He came around eventually.
*** [[spoiler:Francie was killed and doubled, and her doppelganger worked for a season as a bad guy]], and when she was revealed, Sydney would have seen it as a face-heel turn (mitigated by the fact that she wasn't really who she looked like).
*** Sydney's mother did this over and over and over. It's not a spoiler because it's a defining trait of her character, and in the end you're never really sure which side she was on.
*** [[spoiler:Vaughn]] appeared to do this at the end of season 4, but then it's pretty gray as to what's happening. The show has so much of this trope that the audience expected it (or at least was hardly surprised), and then the turn was subverted because he didn't really turn evil.
* On ''Series/{{Lost}}'', Michael was of the WellIntentionedExtremist variety, as he just wanted to save Walt, his son. He felt really bad about it, but there's varying opinion over whether or not we should feel sorry for him.
** Charlie performs his when he kidnaps Aaron and Claire finds out he's a junkie. He had recently fought his demons, won, and turned around from a spoiled jerk to a almost hero. Then they demonize him again. May have involved the writers strike.
** Locke also tagged along with the Others for a while, but he didn't really switch sides (though he certainly came close to being an out and out villain during a portion of Season 4, where his leadership was borderline tyrannical.)
** [[spoiler:Jack in season 5]] to some.
*** [[spoiler:The "some" being irrational Jack-haters. He himself says detonating Jughead to stop the plane crash is the right thing to do because it will save hundreds of lives, but he does have more personal reasons for doing it. In no way are any of his actions "evil".]]
** [[spoiler:Claire and Sayid in the final season, due to being infected by The Sickness. Both eventually fight their way out of it in the end.]]
* Gul Dukat of ''Series/StarTrekDeepSpaceNine'' starts off as a recurring annoyance, but [[HeelFaceTurn gradually warms up to the crew]] and looks like he's on the road to BadassDecay... then he realizes GoodIsDumb and stabs everyone in the back.
** Gul Dukat was one of the more interesting 'grey' characters (along with fellow Cardassian Garak). Most of Dukat's crimes were committed way before the series started, so the fans would not automatically hate him along with Kira Nerys. It was more of case the [=DS9ers=] were warming up to ''him'', especially when he embarked on his [[spoiler:one-bird-of-prey crusade against the Klingons]]. But as soon as he is sees the chance to 'make Cardassia strong again' (i.e. get himself into a position of power again) he does indeed remind everyone that sometimes GoodIsDumb.
** Eddington is a more straightforward example from ''Deep Space 9''.
* ''{{Buffyverse}}'':
** Angel in Season 2 (starts with "Innocence"), Willow in Season 6 (starts in "Seeing Red") and Faith in Season 3 (starts in "Bad Girls" and continues with "Consequences"). All three get subsequent {{Heel Face Turn}}s.
** Angel's FaceHeelTurn happened due to having what is later described as a "moment of perfect happiness" which was his night with Buffy. This activated the CurseEscapeClause which brought back his original self, the incredibly evil Angelus.
** Angel's evil alter ego is used several times on [[Series/{{Angel}} his spinoff]], to the extent that he's now HeelFaceRevolvingDoor.
*** This is more JekyllAndHyde with Angel, as it is stated quite clearly that the two are mutually exclusive. Angelus hates his Alter Ego and considers him weak because he won't feed from humans.
** Willow's FaceHeelTurn came about due to her going crazy after Warren accidentally killed Tara while trying to gun down Buffy. She corners and kills Warren in [[CruelAndUnusualDeath exceedingly cruel fashion]] and then goes after the others, until she eventually [[JumpingOffTheSlipperySlope Jumps Off The Slippery Slope]] and tries to [[OmnicidalManiac destroy the world]].
*** Willow's is far more this trope than Angel as she was always the same person (albeit far, far more angry). She even says later that she remembers exactly how it felt and why she was doing it - and that it felt pretty good. Dark Willow is Normal Willow on the ultimate despairing rage power trip.
** Giles in "The Lost Slayer" novel BizarroWorld, in his vampire version.
*** Not exactly, as per {{Buffyverse}} mythos, vampires are [[DemonicPossession demons that have taken over a human's body]] after the [[SoullessShell human soul has departed]], and thus are not considered the same person once turned. Angel and Spike were special exceptions, arguably considered [[SplitPersonalityMerge demons cohabitating with human souls]].
** Riley in the comics.
*** Except not really. He was spying for Buffy.
* Jake Straka, for some reason, near the end of ''The Guardian''.
* Tyr on ''Series/{{Andromeda}}'' - though we all knew it would happen sooner or later, as Tyr was always [[MagnificentBastard playing his own game]].
* Every character on ''Series/{{Charmed}}'', at some point or other.
** Subverted with It's a Bad, Bad, Bad, Bad World, where the entire WORLD takes a face heel turn, excluding the [[spoiler: demons, which all take a HeelFaceTurn]]
* Agent Lee on ''Series/{{NCIS}}'' appears to be TheMole, faking a relationship to gain access to a private area (of the complex, you pervs) and killing another agent to protect herself. [[spoiler:She's actually being forced to do it by [[IHaveYourWife her niece's kidnappers]]. Naturally, RedemptionEqualsDeath for Agent Lee.]]
* Undersheriff [=McKeen=] on ''{{CSI}}''. Also Detective Vega.
* on ''{{CSI NY}}'' Marty Pino,who went from recurring coroner to drug dealer processing body parts from victims for the drugs they contained.
* Dr. Zack Addy, who turned out to be the serial killer's apprentice on ''{{Bones}}''. [[spoiler: He didn't actually kill anyone and it's more of a case of a weak will being overpowered by a strong one, but only Sweets knows that Zack prefers to be thought of as insane since he wouldn't survive prison. Regardless, his friends still love him (to the confusion of his replacements)]]
* Sweet-natured Kes returns to ''[[Series/StarTrekVoyager Voyager]]'' to crumple bulkheads and anonymous ensigns in "Fury". It turns out she's angry at her former friends because...well it's never really explained. But don't worry as [[ResetButton everything's back to normal by the end]].
** Kes was supposed to be upset over being talked into leaving all of her people and life behind to travel to the middle of nowhere with Voyager's crew, and the episode's plot was about her trying to go back in time and convince her younger self to bail while she still had the chance. Given her AscendedToAHigherPlaneOfExistence exit in "The Gift," it was likely a case of WithGreatPowerComesGreatInsanity.
* ''StElsewhere'''s Dr. Peter White winds up being a serial rapist.
* In the reimagined ''Series/{{Battlestar Galactica|Reimagined}}'', [[spoiler:Felix Gaeta leads a failed mutiny against Admiral Adama, resulting in his and Zarek's deaths]].
** Earlier on in the series, [[spoiler: Boomer [[HeelFaceRevolvingDoor appears]] to have joined Cavil's side in the Cylon civil war, later helps the final Cylon escape from exploratory brain surgery and gives her lover a literal [[ImagineSpot Imagine]]/HopeSpot then steals her "twin's" daughter only to [[PetTheDog bond]] with her "niece" and give her back and is finally killed by her "sister"]].
* Nick in ''Series/TheSecretCircle'', though Melissa finishes him off to save Jake.
* Shane Vandrell in ''Series/TheShield'', more than once.
* In the final season of ''Series/BurnNotice'', [[spoiler:Michael Westen goes deep undercover for the CIA to capture a criminal, James Kendrick. During his time undercover, Michael learns that James is a WellIntentionedExtremist who made it his mission to go after the villains that the government wouldn't. Michael doesn't agree at first, but slowly becomes impressed with James' way of doing things. When the time comes to finally apprehend James, however, Michael learns that the leader of the extraction team is none other than AxCrazy murderer Simon Escher. After Michael kills Simon, he reveals the truth to James, betraying the CIA, the agency that burned him and put a psychopath like Simon in charge.]]
* ''Series/TwentyFour'' embodies this trope. Most seasons have at least one of TheMole at some point. Sometimes this turns out to be misleading, with a few {{Fake Defector}}s, but there are several infamous true face heel turns. Going back to the first season was [[spoiler:Nina Myers, who turns into a recurring villain for two more seasons]]. Most recently was the even more drastic [[spoiler:Tony Almeida, whose HeelFaceRevolvingDoor led the audience to be surprised by the (second) revelation that he was a villain, despite the fact that this was technically common knowledge months before the season even began]].
** A surprising one is that [[spoiler: Jack Bauer himself]] undergoes something of one in the final season. After [[spoiler: Renee Walker]] is killed and he gets screwed over by [[spoiler: President Taylor when she effectively sells her soul to Charles Logan and undergoes her own FH Turn]], he sets out on his own. Initially it seems like he's still trying to just do the right thing and expose the cover-up that [[spoiler: Taylor's]] involved in, but when he murders [[spoiler: Dana Walsh]] in cold blood even though she wasn't directly tied up with what happened to [[spoiler: Renee]] it becomes clear that all he's after is vengeance regardless of the consequences. He gets so consumed he nearly starts World War III solely in the name of revenge, and it takes Chloe to [[spoiler: literally talk him down at the eleventh hour. But by this point his actions have still effectively screwed him over and left him an international fugitive]].
* [[spoiler: Allan]] in season 2 of the new ''Series/RobinHood'', at least until [[spoiler: his HeelFaceTurn]] later on in the season.
* Professional IdiotBall handler [[spoiler: Stuckey]] in the 2009 season finale of ''LawAndOrderSpecialVictimsUnit'' [[spoiler: subverting NarrowedItDownToTheGuyIRecognize. After That Yellow Bastard and Simka Graves, I for one didn't suspect ''the guy who'd been there since the beginning of the season'']].
* ''Series/DoctorWho'''s own 10th Doctor went a little overboard (shall we say) in the episode "The Waters of Mars" when he finally realized he was the only Time Lord left in the Universe and didn't have to follow their rules anymore. He became megalomaniacal, the "Time Lord Victorious!" until the episode's heroine corrects his mistake. [[spoiler: By killing herself.]]
** This is played straight with the Time Lords, led by [[DepartmentOfRedundancyDepartment Lord President of the Time Lords]] Rassilon, turning into [[OmnicidalManiac Omnicidal]] [[KnightTemplar Knight Templars]] with the Time War, leading to the destruction of most of the Daleks as well as the Time Lords, [[EarthShatteringKaboom including Gallifrey]], by the Doctor.
* ''AshesToAshes'' Season 3 kicks off with [[spoiler: the introduction of new DCI Jim Keats. He seems like an upright, intelligent guy who even Gene Hunt begrudgingly respects - mainly because Keats is allowing Hunt to operate the way he wants to operate and isn't interfering the way other [[InternalAffairs IAB officers]] would. He repeatedly tells Alex that he wants to help her, and he knows she has a larger purpose in this world. He makes overtures to the rest of the CID gang - Chris in particular - even bringing over a bottle of champagne to celebrate their closing a case. And then, about five minutes before the end of the episode, he walks into Gene's office, closes the door, and delivers one of the most [[BreakThemByTalking scathing denouncements of Hunt and his people]] we've ever heard, and [[InspectorJavert vows to bring Hunt down]], no matter what.]]
* ''{{Chuck}}'': Daniel Shaw is an all-American hero, willing to die for his country, but [[spoiler: when he finds out thanks to the Ring that Sarah killed his wife, he joins the Ring setting on killing Sarah for revenge; this turns out to be fatal, as Chuck kills him in order to protect Sarah]].
** [[spoiler: Shaw does survive, though not without super-advanced medical help, and returns later on a grand plan to take over every major American intelligence agency while framing his former allies as traitors before executing them. If that wasn't enough, he gets his own Intersect and kills Chuck's dad.]]
* In the 1998 ''Film/{{Merlin}}'' series, [[spoiler: Lord Lot and Morgan Le Fay]] both turn against Arthur and Merlin.
* As of the finale of season 3 of the BBC's ''Series/{{Merlin}}'', [[spoiler:Morgana has finally completely turned against Arthur, Merlin and the rest of Camelot, and, with the possible death of Morgause, is in a prime position to take over as the BigBad of the next season. Technically she was an enemy right from the beginning of season 3, it's just that now ''everyone'' knows about her Face Heel Turn instead of just Merlin and Gaius (and Gwen later on)]].
** The "face-heel-turning" actually begins that the ''start'' of Series 3 [[spoiler: after Morgana returns to Camelot after going missing for a year and becomes TheMole for Morgause and begins doing things like killing people in cold blood and threatening Merlin who unwittingly provokes her move to the dark side by attempting to kill her (for valid reasons) at the end of Series 2.]] The face-heel-turning of [[spoiler: Morgana]] is amplified by the fact the first two seasons spend extensive time establishing the character as sympathetic and on a few occasions heroic.
** In Series 5, [[spoiler: Mordred]] goes from the Adorkable, loyal youngest knight to [[spoiler: Arthur's killer]] after [[spoiler: the girl he loves is executed for trying to kill Arthur.]]
* In the miniseries ''ThumbWrestlingFederation'' (this sorta fits here), former Dextera member Evil Ira left for the Sinistras, simply because being good while he has evil in his name was too confusing.
* In ''{{Smallville}}'': [[spoiler: [[LexLuthor Oh you]] [[ForegoneConclusion highlighted this.]] [[SchmuckBait For shame!]]]]
** Other FHT include [[spoiler: [[SuperPoweredEvilSide Davis Bloome/Doomsday]], [[MommasBoy Jason Teague]], and after a round of HeelFaceRevolvingDoor, [[ColonelBadass Major Zod]].]]
* In season 6 of ''Series/{{Supernatural}}'', the Big Bad of the season, to whom both [[spoiler: Crowley and Eve]] played DiscOneFinalBoss, is revealed to be [[spoiler: Castiel, who has decided that to defeat Rafael and put Heaven on the right track, anything is acceptable - in this case, taking on a million souls. The Winchester boys do their best to stop Castiel throughout the final episodes of the season, while he continues to plead for them to accept him and his reasons for evil]].
* Stefan Salvatore from ''Series/TheVampireDiaries'' at the end of season two and for most of season three. Klaus reverted Stefan into his darker alter ego, the Ripper.
* Duncan [=MacLeod=] does this for two episodes in ''HighlanderTheSeries'', while he's possessed by the Dark Quickening. His good and evil sides finally battle after Methos drags him into a magical hot spring, and his goodness wins, enabling a HeelFaceTurn.
* {{Eastenders}} - James Wilmott-Brown started out as the friendly face of the brewery, then bought his own bar, got obsessed with barmaid Kathy, and eventually raped her.
* Arguably the central plot of ''Series/BreakingBad'' which follows the journey of Walter White across five seasons from kindhearted chemistry teacher and family man suffering from cancer to a fairly loathsome VillainProtagonist [[spoiler: who wouldn't hesitate to poison a child.]]
** [[spoiler: Gets surprisingly flipped halfway through the fifth season when Walt, having reached the top of his empire, having taken his operation global realizes that he has made more money than he could ever hope to spend and far more than he even set out for initially. This leads him to decide he is out of the game, make amends with his former business partner by giving him the money he's owed and try to start over fresh with his family. [[NoGoodDeedGoesUnpunished And then his DEA agent brother-in-law finally figures out he's drug dealer.]]]]
* Forms the basis of the main plot of ''{{Series/Homeland}}'', with a CIA agent convinced that a formerly imprisoned U.S. Marine has been turned into a terrorist during the years of torture he'd endured.
* ''TrueBlood''
** Debbie Pelt performs a HeelFaceTurn offscreen after season 3 and then this trope (onscreen) in season 4.
** [[spoiler:Bill Compton started working for the Vampire Authority and went from mainstreamer to full-on Vampire Bible fanatic, slaughtering humans everywhere and doing all in his power to make vampires the dominant force on the planet.]]
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