[[quoteright:350:[[Franchise/StarWars http://static.tvtropes.org/pmwiki/pub/images/pupil_7360.jpg]]]]
[[caption-width-right:350:[[CallForward "Why do I get the feeling you're going to be the death of me?"]]]]

->''"A young Jedi named Darth Vader, who was [[TropeNamer a pupil of mine until he turned to evil]], helped the Empire hunt down and destroy the Jedi Knights."''
-->-- '''[[TheObiWan Obi-Wan Kenobi]]''', ''Film/ANewHope''

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, resulting in an OlderHeroVsYoungerVillain scenario. More often, the protagonist is another student the mentor takes on. If that's the case then the other student is the MentorsNewHope and the former student is a HerosEvilPredecessor. A long enough MasterApprenticeChain might include a story of one of these as a precautionary tale.

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

Contrast TreacherousAdvisor, which is when the ''mentor'' betrays the student.

Not to be confused with EvilEye or HellishPupils. This is "pupil" as in a student, not part of an eye.

'''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.'''


[[folder:Anime and Manga]]
%%* In ''Manga/{{Alice 19th}}'', Darva was originally Master Lotsuan's disciple.
* In ''Manga/SoulEater'', Asura was Shinigami's apprentice [[spoiler:and as it turns out, son]] 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:Even after his talk with [[FounderOfTheKingdom Hashirama]], he still planned on killing all the Kages and taking over the Leaf Village after the war was over, requiring Naruto to beat even more sense into him. ]]
** 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 DragonInChief 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 knew that he had turned evil, or that he was even ''alive''.
%%* Enchu for Chief Page in ''Manga/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 the mentor role here with CallingTheOldManOut. Ed gets to be the [[MasterApprenticeChain the third link in the chain]] 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 ''Anime/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]].
* ''Literature/DemonCityShinjuku''. Levih Rah was once the student and ally of his master Agni Lai, who taught him the art of Nempo. Unfortunately he was envious of the power of other men and ended up selling his soul to the demons of Hell in return for vast power.

[[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 ''ComicBook/TheAmazingScrewOnHead'': Emperor Zombie used to be Head's manservant until he turned to evil.
* Inverted in ''Comicbook/DeathVigil'' by [[spoiler: Wulf, who was Sam's mentor in the Vigil. Wulf was a loyal and respected member of the Vigil for centuries, but then his gifted surrogate daughter was killed in an accident and Bernie was unable to do anything for her. Although we never hear her reasoning from ''Bernie's'' perspective, Wulf claims she refused him, and [[FaceHeelTurn didn't take it well]]]].
* Franchise/{{Batman}} has Jason Todd, the second Robin who died and came back later wearing a different mask, although whether he wants to (lethally) simply stop all crime from Gotham or murder the whole Batfamily depends on the writer.

[[folder:Fan Works]]
* ''FanFic/ThePiecesLieWhereTheyFell'': Unusually for this trope, it’s the student herself who explains this rather than the teacher - [[spoiler:Sunset Shimmer reveals she was once Princess Celestia’s personal student, until the Princess felt she wasn’t “worthy” and “forced her out”.]]

[[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/MyLittlePonyEquestriaGirls2013'', Sunset Shimmer is a former pupil of Princess Celestia (and Twilight Sparkle's predecessor in that role). When Celestia's tutelage did not turn out to be [[EvilIsEasy the easy path]], she "turned cruel, dishonest and rebellious," abandoning her studies and pursuing power in more unsavory ways. [[spoiler: Unlike most she is [[HeelFaceTurn redeemed]], though she has yet to return to face Celestia.]]

[[folder:Films -- Live-Action]]
* The Vietnamese gangster in ''Film/BigStan'' was The Master's star pupil. From the moment The Master calls Stan "My second best pupil", we just know this trope is going to be invoked!
* Betelgeuse in the movie ''Film/{{Beetlejuice}}'', worked for afterlife case worker Juno before he became a "freelance bio-exorcist."
* Inverted in ''[[Film/BillAndTed Bill And Ted's Bogus Journey]]'', where it is Rufus's old teacher (even if for gym), [[SignificantAnagram De Nomolos]], who turns to evil.
-->"I worked within the system until I could stand it no longer.''
* In ''Film/ChildsPlay'', series BigBad Chucky was originally mentored in his HollywoodVoodoo by a man called Dr. Death, who in spite of his ominous name intended for Chucky to use said voodoo for... well, one struggles to think of any purpose for a BodySurf ritual ''other'' than abusing it willy-nilly, bit evidently Dr. D had one in mind. He becomes outraged when he learns what Chucky has done, but due to being TooDumbToLive quickly comes down with a terminal case of death-by-voodoo-doll.
* Franchise/MarvelCinematicUniverse:
** In ''Film/AntMan'', Hank Pym had mentored Darren Cross but Cross grew resentful that Hank was unwilling to share his research on the Pym Particles and is driven to get the same results from the Pym Particles to prove he was better than Hank, leading him to [[spoiler: supply HYDRA with weapons]].
** In ''Film/DoctorStrange2016'', Kaecilius, a pupil of The Ancient One, goes rogue and recruits followers, steals a page from the Book of Cagliostro, and attempts to summon Dormammu of the Dark Dimension.
** In ''Film/ThorRagnarok'', Odin's firstborn and apprentice Hela worked with him to conquer the Nine Realms. However, when she was not content to stop at nine, he imprisoned her in Hel.
* Han, the BigBad of ''Film/EnterTheDragon'', was a student at the [[PacifistDojo Shaolin temple]] until he became an organized crime boss. [[Creator/BruceLee Lee]], a more loyal student of the temple, is sent to stop him.
--> '''Lee:''' [[TranquilFury You have offended my family, and you have offended the Shaolin temple.]]
* The plot of ''Film/TheHunted'' involves Creator/TommyLeeJones's character being asked to hunt down his former pupil, played by Creator/BenicioDelToro, who has gone rogue.
* Inverted in ''Film/TheMightyDucks'' between Gordon Bombay and Jack Reilly.
* Tommy Gunn from ''Film/RockyV'', 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.
* In ''Film/TheSorcerersApprentice'', Veronica, Balthazar Blake and Horvath were pupils of Merlin, until Horvath went rogue and betrayed them to [=Morgana LeFay=].
* In ''Franchise/StarWars'', Anakin was a good man, if arrogant and quick to anger, until he was seduced by the dark side. Much of Luke's arc is if he will go the same path.
** The TropeNamer is 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]].
** Also inverted by Vader at the end of ''Film/ReturnOfTheJedi''
** Mirrored in the prequel trilogy with [[TheStarscream Dooku]], who was [[TheYoda Yoda's]] pupil before his FaceHeelTurn.
** And now gone full circle in ''Film/TheForceAwakens'' with Kylo Ren, one of Luke's students ([[spoiler:and his nephew by way of Han and Leia, whose real name is Ben Solo]]), going to the Dark Side ([[spoiler:in part thanks to his obsession with his grandfather, the TropeNamer]]), slaughtering his fellow students, and serving the [[TheRemnant First Order]] in an attempt to defeat the New Republic. Ren then [[spoiler:kills Han]]. [[FromBadToWorse Then, things get worse]] in ''Film/TheLastJedi'', when [[spoiler:[[TheStarscream Kylo decides to kill Supreme Leader Snoke]] and [[KlingonPromotion makes himself the new Supreme Leader]].]]
* 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.
* In ''Film/XMenFirstClass'', the mutants all train together as part a CIA team to fight [[BigBad Sebastian Shaw]], but Angel Salvadore decides to join the Hellfire Club shortly after she is recruited by the program. At the end of the film, Magneto and Mystique, after defeating Shaw, form the Brotherhood and become the new Big Bads, turning against Charles Xavier, whose ideas about mutant-human relations differ from the ones they have.

* Sauron, the principle antagonist of Tolkien's ''Literature/TheLordOfTheRings'' trilogy, was a Maia in the First Age under the tutelage of the Vala Aulë 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.
* This is [[DiscussedTrope discussed]] in ''Literature/TheInheritanceCycle''. Neither of Eragon's teachers, Brom or Oromis, taught the BigBad of the series, Galbatorix. Oromis says he's glad for it because Galbatorix made sure to personally kill anyone that was involved in his teaching.
%%* [[SdrawkcabName Nuihc]] for Chiun from ''Literature/TheDestroyer''.
* A number of Luke Skywalker's Jedi students in Franchise/StarWarsLegends end up eventually falling to the Dark Side. He's able to bring some of them back.
** Kyp Durron, a young man in the ''Literature/JediAcademyTrilogy'' purportedly even stronger in the Force than the Skywalkers, is seduced to the dark side by the ghost of the ancient Sith Lord Exar Kun and takes a leftover Imperial superweapon on a bloody rampage against the Imperial Remnant before the other apprentices destroy Exar Kun and Han and Lando are able to talk Kyp down. In later books he becomes TheAtoner.
** 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 ''Literature/TheNewRebellion'' parts written from Brakiss's point of view suggest that he'd like that, but [[DoomedByCanon it's not to be]]: [[spoiler:Brakiss is on the receiving end of a HeelFaceDoorSlam courtesy of a surviving Imperial Royal Guard at the end of the Shadow Academy arc in ''Literature/YoungJediKnights'']].
** Dolph Kueller in ''Literature/TheNewRebellion'' is never really clearly explained [[spoiler:and dies at the end of his only appearance]].
** Alema Rar, debuting in ''The Literature/NewJediOrder: Star By Star'', suffers a CynicismCatalyst in the form of witnessing her identical twin sister being killed by a Yuuzhan Vong creature bred to hunt and kill Jedi, and becomes an advocate of purportedly un-Jedi-like tactics against the Vong (e.g. using leftover Imperial superweapons). In ''The Literature/DarkNestTrilogy'' Luke ultimately expels her from the Order over her behavior, [[spoiler:and she spends the trilogy as the GoldfishPoopGang before being unceremoniously EatenAlive by a critter]].
* Inverted in ''Literature/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.]]
* Subverted, then averted in the ''Literature/WarriorCats'' prequels. Gray Wing acts as a mentor and father figure to Thunder, [[spoiler:his nephew.]] The reason behind this is because Clear Sky [[spoiler:Thunder's father]] was slowly turning into a cruel AntiVillain . When Gray Wing allows Thunder to visit him, Clear Sky claims custody of [[spoiler:his son,]] who was young and naïve, and decides to mentor him. Gray Wing is powerless against this, and fears that Thunder would be influenced and turn cruel. [[spoiler:Averted when Thunder deserts and disowns Clear Sky, seeing the error of his ways. Clear Sky eventually regains his senses, and the (three sort of) make up.]]
* PlayedForLaughs in ''Literature/RulerOfTheMagicalKeys'', where the pupil in question is a cat who learned only one spell – the one that could turn anyone and anything into a mouse – and just went on searching for a good supper and [[KnightTemplar getting rid of evil dogs]].
* In ''Literature/TheWitchlands'', Evraine thinks this way of Aeduen, her former disciple, as she believes he was making good progress as a Carawen WarriorMonk before he joined Ragnor's side. This being said, this is a world of GrayAndGrayMorality.

[[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.
* Inverted with Master Eubulon in ''Series/KamenRiderDragonKnight''.

[[folder:Professional Wrestling]]
* This was the dynamic between Wrestling/BrunoSammartino and Larry Zbyszko in the early 1980s.
* The entire [[Wrestling/TheNexus Nexus]] - except for Wrestling/DanielBryan - turned out to be this.
* Chief Jay Strongbow was always a face, while his protégé Tatanka had two heel runs.
* Both subverted and inverted ("a pupil of mine until I turned good") in the case of the two female members of the Wrestling/TheInvasion. In the partnership of Wrestling/TorrieWilson and Wrestling/StacyKeibler it was apparently the latter who was the junior partner, with Wilson giving Keibler a demeaning slap on the buttocks to get her moving just before their Bra & Panties Match against Wrestling/{{Lita}} and Wrestling/TrishStratus. But instead of Keibler rebelling against her master, it was Wilson who saw the light, much to Keibler's disgust. By the time the Invasion angle was over, Wilson had established herself as WWE Divas' resident AllAmericanFace - [[HeelFaceRevolvingDoor well, for a time, anyway]] - while Keibler became a successful heel manager and corporate saboteur. In effect, [[KnightsOfTheOldRepublic the Darth Malak to Wilson's Darth Revan]].
* Ian Rotten helped Wrestling/ChrisHero, giving him the most recognition in his career till then in IWA Mid-South, as well as giving him some instruction to improve in wrestling. Hero would go on to turn on Rotten and all things IWA Mid-South just because of a loss to Arik Cannon.
* Wrestling/TommyDreamer found this after taking Colin Delaney "under his wing". This had no resolution in WWECW, in Delaney was released but Dreamer has since had to deal with his misdeeds elsewhere, such as the International Wrestling Cartel.
* Mr. 450 turned on his teacher, Invader #3 in the World Wrestling League after Invader decided attacking Sensacional Carlitos after their Navida Corporativa match, after Carlitos had displayed good sportsmanship, was a step too far.[[/folder]]

[[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.
* In ''TabletopGame/HeroQuest'', BigBad [[DubNameChange Morcar/Zargon]] was a student of [[HisNameReallyIsBarkeep Mentor]] who got fed up with not being taught magic fast enough, read texts forbidden to him in secret, gained great power, and ran off to become the [[EvilOverlord Lord of Chaos]].

[[folder:Video Games]]
* According to [[AllThereInTheManual the manual]] for the original ''VideoGame/BanjoKazooie,'' 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.
* ''VideoGame/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 accidentally gives rise to ''VideoGame/MetalGearSolid2SonsOfLiberty'''s MadBomber, Fatman (real name unknown), a wannabe public enemy who has turned his knowledge toward terrorist bombings. Like any good ''Star Wars'' yarn, Stillman is cut down by one of Fatman's booby traps, leaving the callow, blond hero to finish the job.
-->'''Stillman:''' Microwave. With a 7-foot range. It's not a technique I taught him. Neither was that multi-bomb booby trap. Looks like [[ObiWanMoment he's far surpassed me as far as explosives technique goes.]]
%%* In ''VideoGame/{{Tekken}}'', [[ArrogantKungFuGuy Feng Wei]], whose design is actually ''based'' on evil kung fu villains of the 70s wuxia flicks.
* Uther Lightbringer and Arthas Menethil in ''VideoGame/{{Warcraft}} III'' were much like Obi-Wan and Anakin. Arthas is driven to harsher and eviler tactics to defeat the Undead Scourge over the course of the Human campaign, ultimately taking up the cursed blade Frostmourne and becoming the Death Knight we all know and love and killing Uther during the Undead campaign.
%%* 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.
* In ''VideoGames/WarOfOmens'', Listrata dedicates her life to the task of avenging her parents death. Step 1 of that plan is conquering an island chain (the Phenetik islands) as a thesis. However, her mentor, Ashkar views Listrata as a thug for her treatment of the Phenetikians during her conquest.
* ''Franchise/KingdomHearts'': The first six members of Organisation XIII were pupils to Ansem [[spoiler: the Wise, the king of Radiant Gardens]] who helped him in his research into the Heart. Eventually, they turned on him and turned themselves into Heartless. [[spoiler: Only not really. Only Xehanort and Braig apply. The other Apprentices were forcibly turned into Heartless and were manipulated into joining Xemnas under false pretenses upon becoming Nobodies.]]
* In ''VideoGame/AtlasReactor'', OldMaster Su-Ren views [[{{Ninja}} Kaigin]], who was formerly her student, this way. Given the {{Cyberpunk}} GreyAndGrayMorality of the setting the truth is a little more complicated than that, but it's very clear that the two of them are not on the same side. In a slight deviance from the trope, Su-Ren never considered Kaigin her best student but [[TheUnfavourite rather the opposite]].

[[folder:Web Animation]]
* ''WebAnimation/{{RWBY}}'': {{Inverted|Trope}}. After a leadership coup, the White Fang change from a faunus rights organisation into a terrorist organisation. As one of the leaders, Adam was in a position to school Blake in the new way of doing things. When the pair take part in a train heist, Adam intends to blow the train; upon asking about the innocent humans on board, Blake is concerned to hear Adam reply "What about them?" As a result, she abandons Adam, rescuing the train of people in the process, and goes on the run from the White Fang. She decides to attend to Beacon Academy and train to become a Huntress, someone who protects the people from harm. For betraying him, Adam vows to destroy everything she ever loved, guilt-tripping her into feeling like she's to blame for his actions in destroying Beacon Academy and maiming her team-mate, Yang. It eventually leads Blake to vow to take back the White Fang from him and restore it to its former peaceful model.

* ''Webcomic/{{Weregeek}}'' has it PlayedForLaughs by [[http://www.weregeek.com/2011/03/17/ Dustin and Joel]], which is basically them doing the confrontation talk between Kenobi and Vader in ''A New Hope'', but in terms of being a [[GameMaster Dungeon Master]].
* In ''Webcomic/OurLittleAdventure'', Thomas Stratus was one of [[BigBad Brian Souballo's]] old magic teachers back before Brian went all megalomaniacal.

[[folder:Western Animation]]
* In ''WesternAnimation/AvatarTheLastAirbender'', Admiral Zhao served as this to the firebending master Jeong Jeong.
** In this case it was the master who [[HeelFaceTurn changed sides]], while the pupil remained loyal.
* 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.
* Kuvira of ''WesternAnimation/TheLegendOfKorra'' was once a promising apprentice of Suyin Bei Fong that she treated as one of her own children and was Captain of the guard of Zaofu. After the fall of the Earth Kingdom due to the events of Book 3, the two had a falling out over whether or not Zaofu should militarily pacify the now-fractured Earth Kingdom. Kuvira eventually took Suyin's elder son, her engineer, the security forces as well as Zaofu's richest residents to form what eventually became the [[TheEmpire Earth Empire]].
* Inverted in ''WesternAnimation/MenInBlackTheSeries'' where BigBad Alpha was Kay's ''mentor'' until he came across a powerful and illegal alien device that allowed him to assimilate alien body parts.
* Morro of ''{{WesternAnimation/Ninjago}}'' was once a student of Sensei Wu's, and was the first person that Wu considered might one day be the Green Ninja (this universe's version of TheChosenOne). When this turned out not to be true, Morro became enraged and sought to prove destiny wrong, leading him down a darker path which ultimately left him BarredFromTheAfterlife and trapped in the Cursed Realm as a ghost. Although he serves as the main antagonist of Season 5, [[spoiler: he is [[HeelFaceTurn redeemed]] in the made-for-TV special ''Day of the Departed'' and is allowed to pass on to the true afterlife in peace]].