[[quoteright:350:[[Franchise/StarWars http://static.tvtropes.org/pmwiki/pub/images/pupil_7360.jpg]]]]
[[caption-width-right:350:[[CallForward Well, Anakin, one of these days I fear you'll be the death of me.]]]]

->'''Darth Vader:''' ''"When I left you I was but the learner; now ''I'' am the Master."''\\
'''Obi-Wan Kenobi:''' ''"Only a master of evil, Darth."''
-->--'''''[[Film/ANewHope Star Wars]]'''''

A mentor once had a student, ''who used to be a good person'', and perhaps the mentor's most promising and skilled student ever. That student had a flaw; a seed of villainy that needed a trigger. Usually, it was arrogance about his/her skills, or impatience at not being taught the final skills that the mentor had yet to teach. Then the student [[FaceHeelTurn became a villain]].

Sometimes the mentor is TheProtagonist and will have to take the student down in the story. More often, the protagonist is [[MasterApprenticeChain another student the mentor takes on]]. If that's the case then the other student is the MentorsNewHope.

Compare DeceptiveDisciple (when the student was evil the whole time, just pretending not to be), FallenHero, MerlinAndNimue, and TheParagonAlwaysRebels.

'''Do not put examples unless it was clearly stated the pupil was good beforehand. If it turns out the pupil wasn't, that's DeceptiveDisciple.'''
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!!Examples:

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[[folder:Anime and Manga]]
* In ''Manga/{{Alice 19th}}'', Darva was originally Master Lotsuan's disciple.
* In ''Manga/SoulEater'', Asura was Shinigami's apprentice until he went insane and threatened to destroy the world, and had to be sealed away.
* ''Manga/{{Naruto}}''
** Orochimaru was the Third Hokage's student, considered the village's best ninja when he was in Konoha and 'good' enough to ''cry'' when Dan died. Then got fed up with things and left for his various evil deeds. The Third Hokage notes that he always suspected something was amiss about Orochimaru, so it's unclear when exactly he turned evil, even if he was evil before he left the village (around the time the Third Hokage chose Minato for the position of Fourth Hokage largely because Orochimaru was untrustworthy.)
** There's also [[RivalTurnedEvil Sasuke]], Kakashi's former student who abandoned the Leaf Village to train with Orochimaru, and then goes on a RoaringRampageOfRevenge once that's done. At one point he even allies himself with Akatsuki. [[spoiler:He appears to have made something of a HeelFaceTurn after talking with [[FounderOfTheKingdom Hashirama]], although is true motives are implied to be more sinister than he's currently letting on. ]]
** There's also [[spoiler:Nagato, [[NamesToRunAwayFromReallyFast also known as Pain]], a former apprentice of Jiraiya]]. More of a WellIntentionedExtremist, but he still qualifies because he puts such a ''heavy'' emphasis on the "extremist" part. ''Especially'' since his 'good intention' is to ''invent a chakra nuke and use it so that everyone will be too afraid to go to war for a few generations.''
** Danzo could also be considered sort of an example, as he used to be a student of the 2nd Hokage. While not strictly evil as he [[WellIntentionedExtremist thinks his actions are what's best for the village]], he's pretty much constantly doing morally questionable things and getting involved in DirtyBusiness.
** Then there's [[spoiler:Obito, who became ''Tobi, the leader of Akatsuki and TheDragon to Madara Uchiha''. Like Orochimaru and Nagato, he played a big role in the death of his former teacher.]] However, unlike most examples of this trope, his teacher never even knew that he had turned evil, or that he was even ''alive''.
* Enchu for Chief Page in MuhyoAndRoji, who also taught Muhyo.
* ''Manga/FullMetalAlchemist'' pulls a variation, in that Homunculus kind of mentored Slave #23 from the day he gave him his name...but recognized Van Hohenheim as 'his father.' Given his entire identity is later molded around the fatherly role, this concept is clearly significant to him.
** Thus Hohenheim's part in the finale manages to combine TheObiWan role here with CallingTheOldManOut. And Ed gets to be the [[MasterApprenticeChain third party]] and be 'the lead' when they off his big brother.
** The first anime played with the trope in that ''Ed's'' master Izumi Curtis [[MasterApprenticeChain had trained with]] an old woman named Dante, who turned out to be the villain.
* In ''Manga/DragonBall'', the Turtle Hermit states that the Crane Hermit used to be a fellow student of the mighty Mutaito, who underwent a FaceHeelTurn after seeing the might of [[BigBad Piccolo Daimao]], having apparently decided that BeingGoodSucks.
* In episode 10 of ''SamuraiChamploo'', the gang meets up with a friendly monk who turns out to have been a former martial arts teacher who once taught Shoryuu, the villain of the episode. He had encouraged Shoryuu to travel and hone his skills, but this went horribly wrong, when after learning an amazing technique, Shoryuu became obsessed with proving his greatness by challenging and killing any martial artist he could find.
* ''Manga/RurouniKenshin'': The trope title is almost a word-for-word utterance by [[{{Ninja}} Old Man Okina]] after fully realizing that his most beloved disciple, Aoshi, has fallen entirely to the dark side-- and is in league with [[BigBad Makoto Shishio]], to boot. Specifically, he ask Kenshin to put an end to Aoshi's life. However, in a CrowningMomentOfHeartwarming that also defies BrokenPedestal on Misao's part, Kenshin refuses to do it, he believes that Aoshi still possess a trace of goodness in his heart. A few hard knocks later, [[DefiedTrope Aoshi realizes the errors of his way.]]
* ''Anime/YuGiOhGX'': After his FreakOut, Kaiser Ryo Marufuji defeated his old mentor and stole one of those [[DangerousForbiddenTechnique dangerous forbidden decks]], but the sad part is Sameshima [[NotBrainwashed incorrectly]] thought [[IKnowYouAreInThereSomewhereFight he was in there somewhere]].
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[[folder:Comic Books]]
* In ''Comicbook/DoctorStrange'' titles, it's [[DependingOnTheWriter not quite clear]] whether the Ancient One's other disciple Baron Mordo was this or a DeceptiveDisciple. [[TheAtoner Maybe a little of both]].
* ComicBook/LaQueteDeLOiseauDuTemps has Bulrog; a former student of the knight Bragon who turned mercenary and eventually ends up seeking vengeance on his master.
* A slight variation in ''TheAmazingScrewOnHead'': Emperor Zombie used to be Head's manservant until he turned to evil.
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[[folder:Films -- Animated]]
* In ''WesternAnimation/KungFuPanda'', Tai Lung was not only Shifu's first pupil, but also his [[UsedToBeASweetKid adopted son]]. Tai Lung's FaceHeelTurn was a direct result of their screwed up relationship.
** In ''WesternAnimation/KungFuPanda2'', this can be said of Lord Shen and the Soothsayer, who raised him.
* In ''WesternAnimation/MyLittlePonyEquestriaGirls'', Sunset Shimmer is former pupil of [[Characters/FriendshipIsMagicThePrincesses Princess Celestia]] (and [[Characters/FriendshipIsMagicTwilightSparkle Twilight Sparkle]]'s predecessor in that role). When Celestia's tutelage did not turn out be [[EvilIsEasy the easy path]], she "turned cruel and dishonest," abandoning her studies and pursuing power in more unsavory ways.
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[[folder:Films -- Live-Action]]
* ''Franchise/StarWars''
** [[TropeNamer Named]] for a line in ''Star Wars Episode IV: Film/ANewHope'', about how Obi-Wan describes Darth Vader.
--->'''Luke Skywalker:''' How did my father die?
--->'''Obi-Wan Kenobi:''' A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi Knights. [[FromACertainPointOfView He betrayed and murdered your father]].
** Mirrored in the prequel trilogy with [[TheStarscream Dooku]], who was [[TheYoda Yoda's]] pupil before his FaceHeelTurn.
* Betelgeuse in the movie ''Film/{{Beetlejuice}}'', worked for afterlife case worker Juno before he became a "freelance bio-exorcist."
* Clu from ''Film/TronLegacy''. He took Flynn's original programming for him too far, and warped it. The comic ''Betrayal,'' however, indicates that he [[DeceptiveDisciple probably wasn't all that good to begin with]], and Flynn was just too distracted by the pressures of his life in the analog world to notice until it was much too late.
* Inverted in ''[[Film/BillAndTed Bill And Ted's Bogus Journey]]'', where it is Rufus's old teacher, [[SignificantAnagram De Nomolos]], who turns to evil.
** Somewhat undercut when the audience learns that De Nomolous was Rufus's old ''gym'' teacher.
* In ''Film/XMenFirstClass'', the mutants all train together as part a CIA team to fight [[BigBad Sebastian Shaw]], but Angel Salvadore decides to join with Shaw, shortly after she is recruited by the program. At the end of the film Erik (Magneto) and Raven (Mystique), after defeating Shaw become the new Big Bads and turn against Charles Xavier, whose ideas about Mutant-Human relations differ from the ones they have, to form the Brotherhood.
* The plot of ''TheHunted'' involves Creator/TommyLeeJones's character being asked to hunt down his former pupil, played by BenicioDelToro, who has gone rogue.
* The Vietnamese gangster in {{Big Stan}} was The Master's star pupil.
* Tommy Gunn from {{Rocky}} V, who starts out as Rocky's loyal protege, but becomes bitter when the public sees him as Rocky's puppet, and joins with a sleazy promoter instead.
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[[folder:Literature]]
* Sauron, the principle antagonist of Tolkien's ''Literature/TheLordOfTheRings'' trilogy, was a Maia in the First Age under the tutelage of the Vala Aulė the Smith, and went by the name Mairon, before Melkor the Morgoth corrupted him to his cause and made him his lieutenant. When Morgoth was defeated, Sauron essentially became self-employed and sought to dominate Middle-Earth himself.
* Galbatorix and the rest of The Forsworn for the other dragon riders (Oromis, Vrael) in the ''Literature/InheritanceCycle''.
* [[SdrawkcabName Nuihc]] for Chiun from ''TheDestroyer''.
* A startling number of Luke Skywalker's Jedi students, in the Franchise/StarWarsExpandedUniverse, end up eventually falling to the Dark Side. He's able to bring some of them back. Brakiss intended to be a DeceptiveDisciple, but Luke believed he could be turned; Brakiss started BecomingTheMask until Luke put him through a test which horrified him and caused him to flee. Luke always believed that Brakiss could be redeemed, and in ''TheNewRebellion'' parts written from Brakiss's point of view suggest that he'd like that, but [[DoomedByCanon it's not to be]].
* Inverted in TheSecretsOfTheImmortalNicholasFlamel. Creator/WilliamShakespeare was a pupil of John Dee (the BigBad of the series) but turned to good. Or at least, turned to an ally of the Flamels. [[BlackAndGrayMorality How good this makes him is not that clear]].
* The Darklord Lorthas, former student of High Wizard Aemon in ''Literature/BoundarysFall''. [[AntiVillain He's still not entirely bad.]]
* Ishak for Alanna from the third ''Literature/SongOfTheLioness'' book. However, he never actually got a chance to do much evil, because his first attempt [[spoiler: got him killed by the same sword he was trying to use to kill Alanna.]]
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[[folder:Live-Action TV]]
* Played word-for-word straight by Jarrod in ''Series/PowerRangersJungleFury''. Rio, his counterpart in ''Series/JukenSentaiGekiranger'', follows roughly the same path, but there is no single trigger that causes him to switch: he simply becomes dissatisfied with the progress he's making under the good guys.
** Gekiranger also had the three Kenma, precursor villains who turned on the founder of Beast Fist after their leader learned [[DisproportionateRetribution he was the *second* choice for successor]]. This led to the Kensei sealing them away until Rio and Mele let them out.
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[[folder:Tabletop Games]]
* ''TabletopGame/DungeonsAndDragons''
** TabletopGame/ForgottenRealms setting. Elminster isn't really into it, but he taught a lot of wizards in his years, and the main requirement was the talent, not moral qualities -- it's Mystra's priorities and not that her own avatars never were downright villainous. So... Sammaster -- though after being "certified" by Mystra and before fully going nuts. The Shadowsil -- became an evil archmage, worked in late Sammaster's little club, virgin sacrifices and all that. Raerlin -- the guy has a dubious achievement of saying "Death has come for you at last, Old Mage" twice: once while alive, once as a lich. And so on, and on.
* Horus in ''TabletopGame/{{Warhammer 40000}}'' used to be the most trusted Primarch of the GodEmperor, who treated him like a son. Then Horus gets corrupted by Chaos and leads a rebellion that results in trillions dead, the Emperor in a coma, and the future of the [[TheEmpire Imperium]] in peril.
[[/folder]]

[[folder:Video Games]]
* According to [[AllThereInTheManual the manual]] for the original ''{{Banjo-Kazooie}},'' Gruntilda the witch was a student of Mumbo-Jumbo's until she turned evil... and to pay him back, she turned his head into a skull-shaped metal mask. It seems to have been {{Ret Con}}ned, though, with ''Grunty's Revenge'' (which takes place in the past) has Mumbo Jumbo as an up-and-coming shaman without a pupil... and a face that's still skull-shaped.
* In the backstory of the [[VideoGame/FireEmblemAkaneia first]] ''[[VideoGame/FireEmblemAkaneia Fire Emblem]]'' [[VideoGame/FireEmblemAkaneia game]], Gharnef was once a pupil of Gotoh, the White Sage. However, when Gotoh passed the legendary magic tome Aura on to his other pupil Miloah because Gharnef, while a good man, lacked compassion, he was overcome by jealousy and stole the Darksphere, a cursed artifact that twisted him into the cruel EvilSorcerer seen in the game proper.
* ''TheLegendOfZeldaTheMinishCap'': Said by Ezlo about Vaati, who "became enchanted by the wickedness in the hearts of men."
* Vargas in ''Videogame/FinalFantasyVI'', [[SelfMadeOrphan kills his father]] and master out of the belief that he favored Sabin.
* Demolitions expert Peter Stillman confesses to giving rise to ''MetalGearSolid2'''s MadBomber, Fatman. Stillman poured all of his knowledge into his surrogate son, unaware that Fatman was an obsessive fame-seeker whose infamy would put the Unabomber to shame.
-->"I didn't teach him the most important thing I had to tell him. There are some things you have to pass on. The trick is to know which one. Right... All I taught him were skills. And now I have to stop him from using it to destroy us all."
* In ''VideoGame/{{Tekken}}'', [[ArrogantKungFuGuy Feng Wei]], whose design is actually ''based'' on evil kung fu villains of the 70's wuxia flicks.
* Uther Lightbringer and Arthas Menethil in ''VideoGame/{{Warcraft}} III'' were much like Obi-Wan and Anakin.
* Bob Page to Morgan Everett in the ''VideoGame/DeusEx'' series.
* ''VideoGame/LegendOfLegaia''
** Songi is this to Master Zopu and a RivalTurnedEvil to Gala. Zopu and Maya both state that Songi was a good child, but his pride and anger at always being second best to Gala caused his decent unto evil.
** Kazan's former pupil was the swordsman [[spoiler:Rauss.]] The latter was gradually corrupted by the [[DangerousForbiddenTechnique Ultimate Fang]] into a BloodKnight, and his desire to fight his former master led him to a FaceHeelTurn ending with the master killing his former pupil.
* The Naughty Sorceress of ''VideoGame/KingdomOfLoathing'' can be found in Fernswarthy's ethics class. He wasn't that nice a guy, but she wasn't that good a student either.
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[[folder:Webcomics]]
* ''{{Weregeek}}'' has it PlayedForLaughs by [[http://www.weregeek.com/2011/03/17/ Dustin and Joel]].
* In ''Webcomic/OurLittleAdventure'', Thomas Stratus was one of [[BigBad Brian Souballo's]] old magic teachers back before Brian went all megalomaniacal.
[[/folder]]

[[folder:Western Animation]]
* Fukushima from the ''WesternAnimation/KimPossible'' episode "Exchange" was a student of the Yamanuchi Ninja School. He turned out to betray the school and helped Monkey Fist obtain a powerful weapon. It's not really explored why he did so, either he was already paid by Monkey Fist, or he only turned after Ron came to Japan. He could have felt insulted that Ron received honors that according to him should not be given to "outsiders". Or else he became [[LoveMakesYouEvil jealous of Yori's shows of affection]] for Ron.
* In ''WesternAnimation/DungeonsAndDragons'', the Dungeon Master revealed that Venger was a former pupil. In the unaired series finale Venger is revealed to be Dungeon Master's son.
* ''WesternAnimation/TransformersAnimated''. While never really elaborated on, [[BountyHunter Lockdown]] was once a pupil of [[OldMaster Yoketron's]]. At some point, he abandoned the Cyber-Ninja dojo - only to return, sometime after Prowl joined, to make off with the dojo's protoforms and to kill Yoketron. Oilslick may also apply for this trope, but with the lack on information on his past, it's debatable.
* ''WesternAnimation/{{Ewoks}}''. The second season episode ''The First Apprentice" features Zarrak, who was master Logray's first apprentice before he turned to the dark side.
[[/folder]]

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