->''"Already there used to be six of you and now there are just five. Pretty soon, Jake, it'll be four."''
-->-- [[spoiler:'''David''']], the Sixth Ranger Traitor of ''Literature/{{Animorphs}}''

You're a PowerTrio or FiveManBand who just got themselves a new SixthRanger. Things are looking pretty good right now -- your team is expanding, you're making new friends. Looks like things might change permanently!

Wait, [[StatusQuoIsGod changing the status quo]]? {{Gasp}}, heretic!

Surprise! It turns out your fancy new SixthRanger is evil! He now knows all of your secrets, how to exploit them, and how to push all of your emotional buttons. You've got a new enemy, and the best part is -- you'll have an excuse to keep your team down to a PowerTrio or FiveManBand from now on, so [[StatusQuoIsGod the status quo will remain unchanged]].

Just fair warning, this is a trope about betrayal. The names mentioned below may spoil the emotional drama their moment of betrayal brings. However, since Sixth Ranger Traitors tend not to stay with their adoptive teams for long, that may not exactly be much.

Like the SixthRanger, The Sixth Ranger Traitor is its ''own'' villainous counterpart in a FiveBadBand, instead reflecting the member of the group who betrays the others, either by pulling a HeelFaceTurn, [[HeelFaceMole faking one]], simply for their own ends, or on rare occasions [[BrainWashed against their will]].

The name is derived from SixthRanger. SubTrope of TheMole.



[[folder:Anime & Manga]]
* Kaworu from ''Anime/NeonGenesisEvangelion'', although there's enough visual and in-plots hints about people wondering about him that he was deliberately a mysterious character. His character showed up in one episode, which means the time from Introduction to TheReveal about [[spoiler:his identity as The Last Angel]] was about ''fifteen minutes''. Subsequent versions of the story reveal it even faster, likely because [[ItWasHisSled almost anyone watching a remake will know it anyway]]. ''Death & Rebirth'' reveals Kaworu's betrayal before introducing him! The fact that he's first seen in ''Rebuild of Evangelion'' hanging out with Keel Lorentz is a pretty big indication by itself that he's not on NERV's side in the latest iteration of the story, either. [[note]]there is subversion in that He's not with SEELE or even the Angels, either in the end. He picks to side with the Lilim, and decides to at least buy some time for Shinji to survive. Not much good that did anyway, but it's the thought that counted.[[/note]]
** There's also EVA-03 and its pilot, however the case of their betrayal was unintentional, as an Angel managed to hijack them before they even made a sortie.
* ''Anime/CorrectorYui'' - One of the nearest Yui's friends was the true ChosenOne to be the titular Corrector, but I.R. chose Yui because an error later explained she was then infected by Grosser [[spoiler: its Haruna, and no, its not "a hidden grudge" it was pure MindControl like it was later demonstrated with Shun]] before being recruited after Inukai told everyone in the group about it, then after she tried to leave the group (cause Yui [[StatusQuoIsGod was better for the Correctors]]) Grosser takes her and [[BrainwashedAndCrazy turned her against Yui]], it was fixed on the next episode but she didn't return as a Corrector until the next season.[[spoiler: Haruna is eventually cured by Yui herself in an IKnowYouAreInThereSomewhereFight, goes under temporal retirement (she was still remaining as MissionControl) and, in the second season, [[HesBack she rejoins]] the team as SixthRanger]].
* In the second season opening of ''Anime/ScienceNinjaTeamGatchaman'', the team gets a new G-2 as a replacement for dead [[TheLancer Lancer]] "Condor Joe" Asakura, much to the others' discomfiture. Surprise! He's a Galactor agent. Double surprise! [[spoiler: Joe, BackFromTheDead, kills him.]]
* In ''Manga/DeathNote'', Light Yagami joins the secret police taskforce in charge of finding and stopping Kira, a brilliant but crazy serial killer who's using an ArtifactOfDoom to anonymously murder anyone he deems evil, which can reach triple digits on a single day. Unfortunately, [[LightIsNotGood Light]] ''is'' [[VillainProtagonist Kira]].
** It's played with, in that L, [[BigGood the leader of the task force]], is never in any doubt that Light is Kira - inviting him to join the task force is just a ploy to attempt to prove his guilt. [[spoiler: It works. Eventually. Not that L's around to see it.]]
* [[spoiler:Genpou Saji]] from ''IkkiTousen'' starts like this, manipulating both Rakuyou and Nanyou as a ManBehindTheMan. [[spoiler: [[DefeatMeansFriendship After being defeated, though, he becomes a genuine]] SixthRanger.]] In the anime, at least. The manga's a bit more involved, but [[spoiler:Saji]] was never evil.
* ''Manga/FushigiYuugi'''s Chiriko was really a Seiryu Seishi named Amiboshii.
* Team Trinity in ''Anime/MobileSuitGundam00'' season 1. [[spoiler: Anew Returner ([[ManchurianAgent unwillingly]])]] fills the role in season 2.
* Crona from ''Manga/SoulEater'' is taken in after turning good, then is manipulated back to Medusa to be TheMole.\\
In the anime, [[spoiler:Crona decides to stop working for Medusa and leave the DWMA out of guilt. Maka catches him/her on the way out and convinces Crona to stay and be their ally for the rest of the show.]]\\
In the manga, [[spoiler:Crona disappears just after being discovered, turning out to have been called back by Medusa to her lair. Eventually, Crona kills Medusa, but (as Medusa planned) thought so lowly of him/herself for it that Crona decides to become a Kishin as Medusa planned and cause TheEndOfTheWorldAsWeKnowIt. Maka manages to talk Crona back, but by that point Crona had done so much wrong Crona ended up being a BarrierMaiden for the rest of his/her immortal life as repentance, or until Maka manages to rescue him/her, depending on your personal interpretation.]]
* [[spoiler:Meowth of Team Rocket]] pretends to become a new ally for the heroes of ''Anime/{{Pokemon}} Best Wishes'' for one short StoryArc, but it was just to lure them into a trap in Nimbasa City.
* Played with in ''Anime/SwordArtOnline'': [[spoiler:After losing in a duel to Heathcliff, Kirito is forced to join the Knights of the Blood. After a costly boss raid with [=KoB=], Kirito realizes Heathcliff is actually Akihiko Kayaba, creator of SAO and the one responsible for trapping all the players in the game. His ruse exposed, Kayaba reveals that he was setting himself up to betray the [=KoB=] and set himself up as the game's FinalBoss.]]

* Topher from ''Comicbook/{{Runaways}}''. This was less about not changing the status quo, since the team constantly loses and gains members. Topher's betrayal causes the team to be initially suspicious of SixthRanger Victor, especially since they know he's [[LukeIAmYourFather the son of a villain]] (though they don't know which one for a while) and supposedly destined to [[FaceHeelTurn turn evil]]. Given that every single fricken one of them is the child of at least one, and in most cases two villains, what do ya expect?
** It's also implied to have happened on purpose, because [[spoiler:Alex]] knew all along that Topher was a vampire (or at least evil) and brought him to the Hostel so that the rest of the group could end up fighting him to be toughened up.
* In Grant's Morrison's run on ''Comicbook/{{X-Men}}'', where the core team starts out as a FiveManBand, Xorn [[spoiler:isn't just a traitor, he's Magneto in disguise!]] ([[TheRealRemingtonSteele For a while, anyhow.]]) Change and (perhaps futile) attempts to escape the status quo were major themes in this run. The first to join the ''original'' FiveManBand (not counting the Professor) from the sixties, Mimic, ''also'' betrayed the team.
** '''[[ComicBook/NewMutants New X-Men: Academy X]]'' has an interesting case with this happening to both New Mutants and their rival team at the same time. Both teams were five groups of friends short of one to make full training squad. Icarus was added to Hellions, whom he barerly knew, because Julian convinced him to join, and Wither joined New Mutants after he returned to school. Once FBI tried to arrest Wither, Hellions decided to bust him out and Icarus, realizing how horrible consequences such act would have, contacted New Mutants and both groups fought. Once Wither was cleared of all charges he realized who his real friends are and asked to be re-assigned to Hellions, while Icarus jumped at opportunity to take his spot on New Mutants.
* Nemesis Kid of the Legion in ''Comicbook/{{Legion Of Super-Heroes}}''. He joined the Legion to spy on them for the evil Khund Empire (and later became a member of the Legion of Super-Villains).
* ''ComicBook/MarvelStarWars'' does have regulars added to the cast not infrequently. Most of them work out okay - but [[HeroesWantRedheads Shira Brie]], Luke Skywalker's [[{{Wingman}} Wing Guard]] and incipient LoveInterest, turns out to have been hand-picked by Darth Vader.
* In an example that would have made fans of the original series cry, [[spoiler:Sven]], one of the most popular characters of the original ''[[Anime/{{Voltron}} Voltron: Defender of the Universe]]'' series became this in the 2003-4 Devil's Due DarkerAndEdgier ContinuityReboot.
* Shun-Day was this to the [[ComicBook/LesLegendaires Legendaries]], acting as TheMole to her creator [[EvilSorcerer Skroa]]. She however [[BecomingTheMask become the mask]] and ends up saving the other Legendaries from him. [[TheHero Danael]] agreed to let her go as a gratitude, but warned her that the next time they'd meet, it'd be as enemies.
** Later subverted during the Anathos Cycle when Tenebris, [[DaddySLittleVillain Darkhell's daughter]], joins the team. Her motivations for helping the heroes are selfish, she is known to love her father, and two of the Legendaries (namely Shimy and Gryf) were expecting her to betray them, to the point Shimy tried to [[MurderIsTheBestSolution murder]] her once it appeared she was of no more use. Ironically, it turned out she ''never'' betrayed the team, even when BiggerBad Anathos [[WeCanRuleTogether gave her the opportunity to join her]] [[CurbStompBattle after he single-handed defeated the other heroes]]. After the Cycle, she has become a full-time member of the group.
* The Swordsman, a VillainWithGoodPublicity, joined ComicBook/TheAvengers under orders from ComicBook/IronMan's enemy the Mandarin to sabotage the team. After gaining the trust of most of the team, he planted a bomb in their headquarters. It was after he had [[HeelFaceTurn a change of heart]] and disarms the bomb that he was found out and [[ReformedButRejected the team sent him packing]].

[[folder:Fan Fiction]]
* In ''FanFic/PersonalityConflicts'', this is Tommy's greatest fear. Also played straight with Drew and BadFuture Tasha, but subverted with Ryan.
* In ''FanFic/SeventyTwoHours'', Bo is this to the wrestlers. When he moves to America, he falls in naturally with the sadistic group, but has no interest in slaughtering innocents with the others; he simply can't escape. During a battle with [[LaResistance SABRE]], he not only joins the enemy (pulling a complete HeelFaceTurn in the process) but does so in a way that cripples the enemy attack, saving his new friends' lives.
* Miyako in ''Manga/DeathNote'' and ''Manga/KamikazeKaitouJeanne'' fanfic, ''FanFic/ToKillAThief'' is unknowingly playing for Light's FiveBadBand. [[spoiler:When she realized of what he wanted, she turns her back on him.]]
* [[spoiler: Zeakros]] in ''Fanfic/AceCombatTheEquestrianWar''.
* The [[BadFuture Dark World]] arc of the ''FanFic/PonyPOVSeries'', [[spoiler: Discord's sister Rancor joins him and his minions in fighting the Elements of Harmony's rebellion... only to stab him InTheBack (literally) at the opportune moment, in order to steal Destruction's power for herself.]]
* In [[https://www.fanfiction.net/s/6310457/1/Devil-s-Advocate Devil's Advocate]] [[Anime/DigimonTamers Takato]] joins the [[Anime/DigimonAdventure02 Digidestined]] to help them defeat the Digimon Emperor. However as soon as the Emperor dies Takato plans to [[YouHaveOutlivedYourUsefulness turn on the others and kill them.]]

[[folder:Films -- Live-Action]]
* ''Film/TheLosers'' - [[spoiler: Roque]].
* ''Film/TheExpendables'' - [[spoiler: Gunnar. [[EasilyForgiven They let it slide]] before the [[Film/TheExpendables2 sequel]].]]
* ''Film/SuckerPunch'': [[spoiler: Blondie]].
* ''Film/TransformersDarkOfTheMoon'': [[spoiler: Sentinel Prime]].
* ''Film/TheItalianJob2003'' - [[spoiler: Steve]]
* ''Film/XMenFirstClass'': [[spoiler: Angel, Mystique and Magneto.]]
* Lando Calrissian acts as this at in ''Film/TheEmpireStrikesBack'' but he quickly makes a HeelFaceTurn and becomes a regular SixthRanger
* Although, was he really a traitor or was he simply a puppet politician put in a stranglehold by Darth Vader, with the full power of the Empire to back him up? Or was is that Lando, realizing he'd been lied to by Vader, finally decide to take a stand?
* In ''Film/TheHungerGames'', [[spoiler:Peeta Mellark]] is this to the Career Tributes like the novels below.
* In ''Film/GraveEncounters2'' [[spoiler: Lance]] appears out of nowhere, having apparently survived [[spoiler: the first movie]] and shows up to aid the remaining survivors. Too bad for them he is taking orders from the hospital itself which speaks by scratching words into the walls or following him around invisible in the darkness of the hospital. To make this even worse, he [[spoiler: kills Trevor]] and attempts to escape the hospital himself. [[spoiler: too bad the demons of the hospital double crossed him too.]]

* ''{{Dragonlance}}'' - [[spoiler:Eben Shatterstone]].
* ''Literature/{{Animorphs}}'' - [[spoiler:David]].
* Senna from ''Literature/{{Everworld}}''.
* Franchise/StarWarsExpandedUniverse
** [[spoiler:Jacen]], though it's fairly obvious before he actually becomes a Sith.
** Kyp in the ''JediAcademyTrilogy''.
** In the Coruscant Nights Trilogy, [[spoiler: Dejah Duare]].
* In ''Literature/HarryPotter'': [[spoiler:Severus Snape]] is actually a Sixth Ranger Traitor for a FiveBadBand, earning himself a (sudden) special place in the hearts of many readers who had previously hated his guts.
* In ''Literature/TheHungerGames'', [[spoiler:Peeta Mellark]] is this to the Career Tributes.
* In ''[[Literature/TheInfernalDevices The Clockwork Prince]]'',[[spoiler:Jessamine Lovelace]] betrays the Institute [[spoiler:because of her love for Nate.]]

[[folder:Live-Action TV]]
* Zhane in ''Series/PowerRangersInSpace'' actually disguised himself as a "Sixth Psycho Ranger" in order to confuse ThePsychoRangers.
** To the point, despite the trope name, this really hasn't happened in ''Franchise/PowerRangers''. Sixth Rangers have started as antagonists and even villains, but it's always been due to mind control or the manipulation of the truth.
* The ''Series/{{Torchwood}}'' episode "Adam" had the eponymous mind-altering alien that acting as the team's most trusted member. [[DramaticIrony The viewers know he's the bad guy all along]].
* ''Series/BuffyTheVampireSlayer'':
** In season 3, Faith is introduced as a second Slayer and hedonistic ShadowArchetype to Buffy. It takes a few episodes, but a fatal accident sets her on a spiral into a FaceHeelTurn. She eventually makes a HeelFaceTurn and goes back to being one of Buffy's most important allies, though.
** Rather amusingly, Spike plays the SixthRangerTraitor role in season 4 -- selling out Buffy and the Scoobies to Adam - despite the fact that he makes no bones about being evil and hating the Scoobies the whole time:
---> '''Spike''': Tell you what I'll do then. I'll head out, find this girl, tell her exactly where all of you are, and then watch as she kills you.
---> ''*shocked silence from Xander and Giles*''
---> '''Spike''': Can't any one of your damn little Scooby club at least ''try'' to remember that ''I hate you all''? Just because I can't do the damage myself doesn't stop me from aiming a loose cannon your way. And here I thought the evening'd be dull.
* [[spoiler: Chester Lake]] from ''Series/LawAndOrderSpecialVictimsUnit'' eventually ends up killing a rapist cop who was found not guilty at trial. To [[spoiler: Lake]]'s credit, said cop had previously tried repeatedly to kill him, and in the end he made no attempt to conceal his crime. Much more fitting to the trope is TheScrappy [[spoiler: Dale Stuckey]], who turns out to have masterminded a plot to kill the lawyers and judge in a serial killer's murder trial in order to frame the killer, who he had originally accidentally set free due to screwing up the forensic evidence. He ends up killing the MauveShirt CSI tech, and almost ends up killing Stabler.
* [[spoiler: Leek]] from ''Series/{{Primeval}}''. And Christine. And Philip. If the team (or Nick in series 2, and Abby in series 5) hate somebody, then that person is, guaranteed, to be evil!
* Rick Murray from ''Series/DegrassiTheNextGeneration''. Crazy, check. Ready to explode, check. Attacks his friends, check.
* Jorge del Salto from ''Series/{{Carrusel}}''.
* Oddly enough, the reality show ''Dance Moms'' has an example of this, when [[spoiler:the newest mother to the group, Cathy, defects back to her own dance studio, then decides to directly compete against her erstwhile colleagues in an upcoming competition. She even specifically states that now she's seen the Abbey Lee company from the inside, so she can use their own methods against them, going so far as to steal one of the children's music. Like most Sixth Ranger Traitors, she fails spectacularly]].
* ''Series/{{NCIS}}'' had both [[spoiler: Chip]], who inserted himself into [=NCIS=] as part of a long term scheme to get revenge on Tony for ruining his career years ago, and [[spoiler: Agent Lee]], who was an enemy double agent. For a while the team took it for granted that Ziva was one of these, being a double agent for the Israelis, but she eventually proves her loyalty to the team.
* [[spoiler: Zoey]] from ''Series/HowIMetYourMother'' became one of these, after she grew very close with the gang and even dated Ted. However when [[spoiler: Ted said "no" to preserving an old building called the Arcadian]], said person revealed to have [[spoiler: kept the recording she made of Ted praising the Arcadian]] despite having promised to get rid of it.
* ''Series/{{Revenge}}'': If you go by AlternateCharacterInterpretation, Ashley Davenport, although she also isn't fully aware of her role in Emily's scheming and is at least partially loyal to the Graysons.

[[folder:Professional Wrestling]]
* CMPunk played the good version of this in Wrestling/{{WWE}}'s {{Wrestling/ECW}} revival, infiltrating the New Breed in order to break them apart from within.

[[folder:Religion and Mythology]]
* Judas Iscariot, the UrExample.
* Hushai plays the role of TheMole for King David in the story of Absalom's rebellion. The guy even has the balls to lampshade it ''in front of Absalom''.
* Mordred in the King Arthur mythology

[[folder:Web Comics]]
* ''Webcomic/TheCrossoverlord'': [[spoiler: The Green Avenger was this. Justified, because she was brainwashed by Smiling Man.]]
* Eikre from ''Webcomic/RPGWorld'' was heavily implied to be one of these when he joined the party. [[spoiler:Subverted when it turns out he was [[RedHerringMole on the level]] and the real [[TheMole mole]] was a flower that he bought from a random NPC to give to Cherry.]]
* [[spoiler:[[SquishyWizard Emily]] ]]from ''Webcomic/OurLittleAdventure'' turned out to be a PuppeteerParasite ManchurianAgent of the [[TheEmpire Souballo Empire]].

[[folder:Web Original]]
* In the ''Machinima/YogscastMinecraftSeries'', specifically ''[=MarsQuest=]'' [[spoiler:LetsPlay/{{Sjin}}]] joins up with LetsPlay/LewisBrindley, LetsPlay/SimonLane and LetsPlay/DuncanJones to get to Mars and rescue the captive [[spoiler:LetsPlay/{{Sips}}]]. Once the goal is achieved, he tries backstabbing Team J.A.F.F.A, but this fails ''horribly''.

[[folder:Video Games]]
* ''VideoGame/MassEffect3'' has [[spoiler: Maya Brooks]] in the "Citadel" DLC.
* This is how [[spoiler: Bass]] was introduced in ''VideoGame/MegaMan7''.
* ''VideoGame/MegaManX 4'' - [[spoiler:Double. Not that that is a MeaningfulName or anything.]]
* ''Franchise/FinalFantasy'' series
** In ''VideoGame/FinalFantasyIV'', when returning to Baron, you run into Cecil's old friend Chancellor Baigan. He "joins" your party (despite the fact that your party is already full (the game doesn't ''allow'' six playable characters to be used at once) and he follows along behind you unlike all the other party members who aren't shown on screen during normal gameplay). He is revealed as a monster in disguise about five seconds later. In the DS remake, this is played as a cutscene and Baigan has a new 3D model, and he immediately reveals himself as a monster in the cutscene.
** ''VideoGame/FinalFantasyX'' - [[spoiler:Maester Seymour]], since he joins the party briefly before turning out to be an OmnicidalManiac. (Or, he would be if he wasn't so ObviouslyEvil).
** ''VideoGame/FinalFantasyXII'' offers one for both sides: The heroes get [[spoiler: Vossler]], and the villains get [[spoiler: Gabranth]].
** ''VideoGame/FinalFantasyTactics'' gives us Algus/Argath, the guest for about half of Chapter 1. Also Gafgarion, a guest for several battles during Chapter 2.
** ''VideoGame/FinalFantasyTacticsA2'' gives us [[spoiler:Adelle, though she's merely BrainwashedAndCrazy.]]
* Played with in ''VideoGame/FireEmblemFates''. The Avatar unintentionally becomes one in the Conquest version of the game. Returning to their adopted family in Nohr after being reunited with and fighting alongside their true one in Hoshido for awhile.
* Khunag of ''{{Albion}}'' joins the party as the sixth ranger. He has little role for awhile. Then at one point, the player must infiltrate the cult he once belonged to, and he's the only guide available. He 'guides' the player into declaring war on the cult, slaughtering their best warriors and eventually killing the leader, with whom he had a score to settle.
* In ''[[AlternateUniverse Another Day]]'', the bonus chapter of ''VideoGame/TheWorldEndsWithYou'', [[spoiler:Rhyme]], of all people [[note]]this is the insanity that is ''Another Day''[[/note]] pulls this on Neku...er, Shuto's [[FiveManBand team]] of Tin Pin Slammer-playing heroes.
* [[spoiler:Yoshimo]] from ''[[BaldursGate Baldur's Gate II: Shadows of Amn]]''.
* Harle in ''Chrono Cross'', twice, betraying Lynx for you because [[spoiler:you are Lynx]] and then betraying you for [[spoiler:the Dragons]] after you beat FATE.
* Aydana Kozlova in ''[[GhostRecon Ghost Recon: Shadow Wars]]'' is a subversion of this trope. [[spoiler: She seemed to betray the team and released the enemy that TheSquad had just captured. It turns out that she only released him so the team would be able to track him down and lead them to the BigBad. Then she joined back your team and was EasilyForgiven.]]
* Dark Pit from ''VideoGame/KidIcarusUprising'' was created by Pandora to be an EvilKnockoff of [[TheHero Pit]] who'll fight for the Underworld Army. 10 seconds after his creation, he defects and becomes a neutral WildCard during most of the game [[spoiler: until he joins with Pit near the end of the game.]]
* [[{{TheDragon}} Courtney Gears]] in ''VideoGame/RatchetAndClankUpYourArsenal''. At first, it looks like she agrees to assist the Q-Force in helping out with their battle against [[{{BigBad}} Dr. Nefarious]], but soon [[{{FaceHeelTurn}} betrays the team]] [[spoiler:by kidnapping Clank and using Skidd as a test subject for the Biobliterator in her lair, the Obani Draco]]. She soon [[{{DisneyVillainDeath}} meets her end]] at the hands of Ratchet, but is [[{{DeathIsCheap}} later restored]].
** [[VideoGame/RatchetAndClankFutureToolsOfDestruction Rusty Pete]] may also count, since he only allys himself with Ratchet to [[spoiler: find the body of Angstrom Darkwater so that he can revive Captain Slag]].
* [[spoiler:Onef]] of ''VideoGame/TheBannerSaga''. Is recruited from [[spoiler:Frostvellr]], and fills out this role in the party. Invariably turns on the party later on, as [[{{Foreshadowing}} pointed out]] by their class title [[spoiler:"Backbiter"]]. Ends up killing a good number of your clansmen along with [[spoiler:Egil]], and [[spoiler:Oddleif]] comes scarily close to dying as well.
* UltimaV has [[SdrawkcabName Saduj]] who can join your party, but it turns out he's a spy for the BigBad, not just that but he'll flee every battle you enter massively dropping your karma eventually making the game unwinnable. Really the only use for him (Without him having to join) is that he's the only clue to the existence of the Sandalwood Box that is one of many items you need to beat the game, and that you can make him a [[UriahGambit Hairu]] in a particular battle.
* Inverted in ''VideoGame/{{StarWarsTheOldRepublic}}''. [[spoiler:The trooper story casts the player character as the newest and only member of their squad to remain loyal after everyone else defects to the Empire.]]

[[folder:Western Animation]]
* Terra from ''WesternAnimation/TeenTitans''. In the original comics, she was TheMole working for Deathstroke, but in the cartoon, she underwent a FaceHeelTurn. If it wasn't obvious enough that Terra as a Titan wasn't going to last long, the episode following her joining the team has her suspiciously absent save a very brief non-speaking cameo in the end, and the title of the next episode when she actually appears as a member of the team? [[SpoilerTitle "Betrayal"]]. And then her next two appearances in which she actually invokes this trope? "Aftershock" (Which is a two part episode).
* William from ''WesternAnimation/CodeLyoko''. Although he is not evil, he got cocky to the point where XANA succeeded in taking him over. The surprise factor was actually legitimate, because the build-up was so long.
* ''WesternAnimation/SuperRobotMonkeyTeamHyperForceGo'' provides somewhat of a twist on this with Mandarin, because he was originally introduced as "The Sixth Monkey," but it's explained in the beginning of the episode that he was actually the leader of the Hyperforce before Chiro and they had to get rid of him because he turned evil.
* In ''GIJoeSigma6'', [[spoiler:Firefly]] ends up betraying the team to Cobra.
* [[spoiler: Longarm Prime]] from ''WesternAnimation/TransformersAnimated'', who is later revealed to be Shockwave in disguise.
* Foxglove from ''WesternAnimation/ChipNDaleRescueRangers'' helped the Rangers mainly so she could steal the episode's PlotCoupons they found, and give them to the villain/goons she worked for... and also because of an affection for Dale, which lead to her HeelFaceTurn back to the Rangers.
** Also, Desiree D'Allure, Monterey Jack's old crush, does this as well... except unlike Foxglove, she ''stays'' evil, and gets away with it! (Well, not completely.)
* In ''WesternAnimation/ThunderCats2011'', [[spoiler:Pumyra is actually a DeadAllAlong FemmeFatale who wants Lion-O dead for accidentally abandoning her to die in the rubble of Thundera.]]
* On ''WesternAnimation/TitanMaximum'', Gibs ''used to be'' the team's SmartGuy and TheLancer. The series starts with his reappearance after disappearing for a few years and announcing that he's the new BigBad in town.
* In ''WesternAnimation/{{Robotix}},'' the Protectons eventually revive another of their [[SealedGoodInACan frozen comrades]] into a [[BrainUploading robot body,]] but unknown to them, Nemesis switched things so the body actually houses the mind of one of his minions, Venturak.
* In the second season of ''WesternAnimation/TheLegendOfKorra'' [[spoiler: Varrick]] is this for a while to the Krew. Even when he begins manipulating and betraying some of the members, it takes them a while to figure it out. Even after he's exposed, he still thinks they're friends. [[spoiler:He does eventually do a HeelFaceTurn a good two books later]].
* Discord pulls this stunt in the Season 4 Finale of ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' after listening to Tirek's HannibalLecture. Getting swiftly backstabbed, [[ManaDrain drained of his powers]], and ''still'' forgiven by his former friends kicks him back to the pony's side for good... [[HeelFaceRevolvingDoor probably...]] [[ReformedButNotTamed hopefully]].