Stealth Mentor

""I am your enemy, the first one you've ever had who was smarter than you. There is no teacher but the enemy. No one but the enemy will ever tell you what the enemy is going to do. No one but the enemy will ever teach you how to destroy and conquer. Only the enemy shows you where you are weak. Only the enemy tells you when he is strong. And the rules of the game are what you can do to him and what you can stop him from doing to you. I am your enemy from now on. From now on, I am your teacher.""

- Mazer Rackham, Ender's Game

The polar opposite of the Treacherous Advisor, the Stealth Mentor is a Trickster Mentor who poses as an antagonist for much of the story but ultimately reveals that all of their actions have been a sneaky way of forcing the hero to become stronger. A subtrope of the Reverse Mole, can overlap with the Mysterious Protector. This character type will inevitably be an Enigmatic Minion to the heroes at some point prior to their reveal. Any losses will be revealed to be intentional.

This can take a couple of forms: either giving the aspiring hero a taste of what he's going to be up against in the big leagues because it's The Only Way They Will Learn, or encouraging a budding rebel by giving him something to push against. Expect generous helpings of Reverse Psychology.

The Stealth Mentor's motives may vary: some genuinely have the hero's best interests at heart, but others may be grooming him as a Worthy Opponent - in the most lethal scenario this may be part of a plan in which My Death Is Just the Beginning.

This is the Training From Hell, and then some, because the hero really believes that this guy is out to get him. If the Stealth Mentor's actions could plausibly have gotten the hero killed (and the Stealth Mentor cares enough for this to be a problem), this is a form of Xanatos Roulette... but the hero survived, as the Stealth Mentor knew he would, so this falls under the Omniscient Morality License.

If a recurring antagonist or Aloof Big Brother is a popular Ensemble Darkhorse, expect lots of Fan Speculation to this effect. It also doubles as a convenient Hand Wave to the question "if he's such a nice guy, why does he keep trying to brutally kill me?"

A lighter variant is the parent who encourages a romance by pretending to vociferously oppose it, as Prospero does in Shakespeare's The Tempest.

Anime and Manga

 * Lots of fan speculation regarding Inuyasha's Aloof Big Brother Sesshomaru, though this is highly debatable.
 * It's speculated that this was the crux of Gendo's plan in Neon Genesis Evangelion : get Shinji to hate him so he can synchronize with Unit 01. Of course, this i heavily debated, given that much is left ambiguous by the Mind Screw. A much straighter example is in Rebuild of Evangelion.
 * Some fans of Ranma ½ might argue that Genma Saotome is one of these who hasn't gotten around to the "big reveal yet", claiming that his various "mistakes" (which include getting his son a Gender Bender Curse while under a Seppuku contract binding him to be a paragon of manliness and trapping him as part of a Love Dodecahedron) are actually very (very) tough love training exercises intended to teach Ranma more cerebral skills. Many more fans, however, would claim that Genma is just a short-sighted, impatient, impulsive, greedy nitwit of a Sink or Swim Mentor who just so happens to have a student that's learned to thrive on Training From Hell and is a born prodigy at Martial Arts and Crafts.
 * is/was apparently one for Sasuke Uchiha in Naruto. He made Sasuke hate him so much that he would spend his entire life training to get strong enough to kill him, and   transferred his strongest techniques to him to protect him   His methods were a little harsher than most of the examples on this page, but he got the job done...
 * Too bad what Sasuke decided to do with this power, really.
 * The 'Lost Episode' of Love Hina reveals that Mokoto's older sister uses this: Initially, she appears to be downright antagonistic and unreasonable, but towards the end it's revealed that she's really just doing it to force Mokoto to grow stronger.
 * This is a near dead-accurate description of Tsuruko's introduction in the manga, although she did have a right to be irritated with the kid.
 * In Soul Eater Dr. Stein is originally posed as a villain who resurrected their teacher, Sid, for experimentation. By the end its all made clear that the plot is part of a remedial lesson.
 * Yu Yu Hakusho: Hiei, a Noble Demon who tries to keep his true loyalties ambiguous, has a tendency to greet Yusuke by randomly attacking him - to test how strong Yusuke has become. Since Hiei was originally recruited into Team Urameshi through a forced Defeat Means Friendship, the first few times he does this Yusuke can't quite be sure he isn't actually trying to kill him.
 * A less benevolent example (also from Yu Yu Hakusho) is Toguro, who has an obsession with making Yusuke stronger in their fights because he wants an opponent against whom he can use 100% of his power. He goes so far as to so that Yusuke's grief and rage will make him fight harder.
 * Genkai set up three Territory Masters to seemingly attack his friends, in the hope that they'd learn how to deal with Sensui's Seven.
 * In Cardcaptor Sakura it's a bit more complex because of Sakura's reaction. The basic trope is there:  is a good guy and a mentor figure, but he creates trouble so Sakura will put her own magic on the Clow Cards (the Cards would die otherwise). On the other hand, Sakura has no idea that he is the one behind this, and treats him as just another of her friends.
 * It's possible that Bartholomew Kuma in One Piece may be this and not as Lawful Neutral as he lead you to believe. It wasn't so much that he spared the Straw Hats, but his next encounter with them, which wasn't too long after their first battle with them,
 * Ovan from .hack Conglomerate is a Stealth Mentor of sorts to Haseo. All his actions in the story are directed at making Haseo stronger than himself
 * Just a side note, Ovan was a straight up mentor for Haseo before their mutual (and very close) friend, Shino, fell into a coma.
 * During the Bount arc of Bleach
 * Also,, who's been teaching Ichigo his honor code and how to fight for years under the guise of being completely and violently insane.
 * And lastly,
 * G Gundam:
 * In the 2003 Astro Boy anime, Mad Scientist Dr. Tenma creates a series of ever-stronger robots to push his estranged "son" to his physical and ethical limits, in order to make Astro into a worthy ruler for robot-kind.
 * If the fifth arc is to be believed, has acted out this role for Battler in Umineko no Naku Koro ni.
 * Scavenger takes this role in Transformers Armada: while undercover among the Decepticons, he puts on a big show of taunting Hot Shot for the latter's lack of skill. This turns out to be a way to sneak him some combat tips.
 * Amnael/ acts this way to Judai in Yu-Gi-Oh! GX, dueling him to test his skill and make sure he's ready for the final battle against Kagemaru. In the dub, Yubel also acts this way to Jaden (in her/his/its own twisted way), believing Jaden tormented Yubel to make her/him/it stronger and doing the same to him. Compared to Amnael, Yubel's mentorship has much more dramatic consequences.
 * Meta Knight in the Kirby anime counted as this early on (before he revealed himself to be good, of course), and was only working for King Dedede to stop the monsters ordered from Nightmare Enterprises/Holy Nightmare Company while keeping on the king's good side. Once Kirby came into the picture, Meta Knight also ended up training him. Of course, King Dedede was so stupid he didn't figure it out, even after The Reveal.
 * Amnael/ acts this way to Judai in Yu-Gi-Oh! GX, dueling him to test his skill and make sure he's ready for the final battle against Kagemaru. In the dub, Yubel also acts this way to Jaden (in her/his/its own twisted way), believing Jaden tormented Yubel to make her/him/it stronger and doing the same to him. Compared to Amnael, Yubel's mentorship has much more dramatic consequences.
 * Meta Knight in the Kirby anime counted as this early on (before he revealed himself to be good, of course), and was only working for King Dedede to stop the monsters ordered from Nightmare Enterprises/Holy Nightmare Company while keeping on the king's good side. Once Kirby came into the picture, Meta Knight also ended up training him. Of course, King Dedede was so stupid he didn't figure it out, even after The Reveal.

Comic Books

 * This is allegedly Zoom (the second Reverse Flash)'s modus operandi. He claims that he wants to make the Flash stronger. Mostly he just goes around killing people -- which is, as luck would have it, exactly what his philosophy calls for. Zoom wants to, as he would put it, "make Walllllly abetterhero thrrrrough tragedyyyy", or by forcing him to deal with tragedy.
 * Mr. Mxyzptlk, reality warping enemy of Superman, is sometimes implied to be one of these, Depending on the Writer.

Film

 * Mr. Miyagi's training in The Karate Kid has been moved to the discussion section; don't think we haven't thought of it.
 * The Joker in The Dark Knight claims to be this to Gotham and more specifically, to . But then again, he is The Joker.
 * Ryan Bingham (George Clooney) in Up in the Air seems to be the hero (or antihero) but he is in fact the mentor to the actual hero, Natalie Keener (Anna Kendrick).

Literature

 * Mrs. Lorelei Granger, the strict teacher in the novel Frindle.
 * Severus Snape displays elements of this, hating Harry but ultimately being one of his best teachers. Snape taught Harry how to duel and Expelliarmus, the spell he's "most famous for", saved Harry countless times, gave him the poison lesson that eventually saved Ron's life, tried to teach the boy how to block out Voldemort's mental influence,, AND even  . Let's not even get into all the things he did in the last book. How could someone be so antagonistic, yet so helpful?   He was torn.
 * In Ender's Game, Mazer Rackham does this to Ender, with the difference that he fully acknowledges his aim from the beginning in the page quote.
 * It's not just Mazer Rackham. Colonel Graff, who is the head of Battle School, uses this as standard operating procedure. He's specifically ordered all the adults in Battle School to do everything they can to make Ender as miserable as possible and never, ever come to his aid - even to save his life.
 * Vergere, of the Star Wars Expanded Universe novels, trains Jacen Solo this way, while pretending to be working for the Yuuzhan Vong, setting up Jacen to bring about their downfall… then she turns out to be a Sith.
 * Jeb Batchelder of the Maximum Ride series of novels does this so many times (and Double Subverts it almost as often) it's almost become an Overly Long Gag.
 * A short story based on Magic: The Gathering featured a wizard who had fought a battle against another for time immemorial. When his opponent surrenders, he finds out that his opponent was his creator and had merely been training him to fight a battle that the creator found too frightening to even contemplate. The story ends with temporary peace having been found with the creator wizard's destruction, but the creation staring out and waiting for the new host to arrive...
 * A short story based on Magic: The Gathering featured a wizard who had fought a battle against another for time immemorial. When his opponent surrenders, he finds out that his opponent was his creator and had merely been training him to fight a battle that the creator found too frightening to even contemplate. The story ends with temporary peace having been found with the creator wizard's destruction, but the creation staring out and waiting for the new host to arrive...

Live Action TV

 * Heroes has a literal stealth mentor: Claude, who teaches Peter how to fully use his power copying ability, has the power of invisibility. And whacking Peter with a broomstick, which is a power many fans wish they had.
 * Chuck:
 * Q in Star Trek: The Next Generation, at least according to the last episode.

Professional Wrestling

 * John Bradshaw Layfield was a Real Life Example for The Miz. He intentionally bullied the Miz to see whether he had what it took to stick it out in the profession.

Theater

 * The musical The Fantasticks has the romantic version.

Video Games

 * In Famous: As it would turn out, big bad Kessler was actually.
 * from System Shock 2, who pretty much uses you to destroy an alien race that's infected the ship.
 * Dimentio in Super Paper Mario. His early monologues and actions reveal that he is trying to secretly help Mario and the other heroes become stronger in order to defeat Big Bad Count Bleck. His motives, however, are less than pleasant. (Unfortunately, this is undermined by the same scene in which he pulls The (fake) Reveal on the heroes. After explaining his intent to defeat Bleck, he asks them for their help. Agreeing repeatedly results in a Nonstandard Game Over. Oops.)
 * That's less of an undermining than it seems. Before and during his request the game drops a few blatant hints (and then, I believe, outright says, since the game lays a lampshade on everything) that he wants to kill Bleck to follow his own plans or world domination, so it's less that the game ruins the Reveal more that it we pretty figured it out (or at least realized he couldn't be trusted) earlier and were waiting for it to be fully explained.
 * This is ProtoMan's MO in the original Mega Man games. In 7 he even gives Mega Man his Proto Shield if he beats him, and admits that his brother has nothing left to learn.
 * Disgaea: Hour of Darkness: Mid-Boss!
 * In Dissidia Final Fantasy, Golbez is given this role, because it would be extremely awkward if after all that happened in his original game, he'd willingly turn his back and smack Cecil around For the Evulz. He's also the only villain who has a different 'death' cutscene, in which he doesn't vanish with dark energy, but just retreats.
 * Nero from My World, My Way is a mentor-in-secret to the game's Spoiled Brat protagonist. The player can even choose what type of "help" he gives her at the end of each level (usually in the form of a quickie boss battle).
 * In the first Super Robot Wars Original Generation game, is a Stealth Mentor. In particular, Sanger Zonvolt is particularly unsubtle that this is his plan, to the extent that none of his teammates ever really think he's betrayed them.
 * is another particularly interesting example, in that he actually begins as a mentor character before betraying the party and revealing that he only helped train the heroes so that they'd be more useful when they were brainwashed and integrated into the Aerogaters' army. He even admits that he's continuing to train them by being their enemy.
 * Waka from Okami.
 * This is pretty much main motive in Tales of Symphonia. And, to a lesser extent,  (although both have other reasons for acting the antagonist).
 * In Lunar 2, plays this role. He's unable to directly oppose the Big Bad himself because  Once the heroes figure out what he's up to,.
 * Grahf in Xenogears
 * Albedo in Xenosaga . Ah, brotherly love.
 * In Castlevania: Lords of Shadow, after aiding you throughout the game All so that Gabriel will be prepared to face the true Big Bad.
 * Although his role varies from game to game, Meta Knight is sometimes implied to be this to Kirby - most notably in Kirby's Adventure, where he shows up to toss Kirby invincibility lollipops about as often as he sends his underlings to attack him.
 * In Westwood Studio's 1997 game based on the film Blade Runner, Graf acts as one to the protagonist Ray McCoy.

Visual Novels

 * Arguably, Archer from Fate/stay night is this to Shirou -- in the anime at least, and in the visual novel.

Webcomics

 * In Sparkling Generation Valkyrie Yuuki,.
 * Vriska in Homestuck uses this justification to explain some of her eviller acts, like giving the main antagonist the powers of a god just so John, her student, would have to become stronger to beat him. Deconstructed in that it's shown to be the egotistical madness that it was, and none of the other characters approve of her actions.

Western Animation

 * Scavenger in Transformers Armada takes this role for a while. During which he helps the Decepticons get their hands on a superweapon (and even makes sure Megatron will use it personally!), which is probably the only reason they believed he was on their side, given that his behavior towards Hot Shot would be downright bizarre if he wasn't secretly an Autobot.
 * It was also pretty cleverly done in terms of the character's physical design. In the G1 series, Scavenger was a Decepticon and transformed into a green and purple construction vehicle. In Armada, Scavenger was a (fake) Decepticon and transformed into a green and purple construction vehicle. The Genre Savvy denizens of the other side of the fourth wall would, of course, jump to the conclusion that he was a Decepticon in homage to the G1 character.
 * Chase Young in Xiaolin Showdown -- but he's trying to convert Omi to evil, so he's not a Reverse Mole.
 * Proto Man in the Mega Man cartoon might be considered one at few times but it's highly debatable (maybe if it would have been finished one could judge reliably.

Real Life

 * In security parlance, a Red Team is a group that launches fake attacks against various assets in order to gauge responses and test security holes. What puts them in this trope is that the attacked group doesn't know that it's a fake attack until it's over (just as they would in real life).