Everybody knows the hero's journey by heart at this point. The chosen one gets called to adventure, refuses, accepts, goes on trials, loses a mentor, faces darkness, defeats evil. But sometimes the hero's journey takes a major detour. Here are 10 hero's journeys go went to a dark, terrible place.
1) Anakin Skywalker
When you make it onto the AFI's 100 Years... 100 Heroes and Villainslist as the third greatest villain of all time, something has probably gone a little wrong with your hero's journey. Anakin's starts off pretty promisingly -- ordinary world, good, call to action, good -- but goes drastically downhill with the whole turning dark side thing. He gets to return to the light in the very end, though, so that's something.
2) Katniss Everdeen
Called to adventure when her sister's name is chosen for the next Hunger Games, poor Katniss embarks, reluctantly, on her hero's journey. Now, plenty of heroes' journeys are littered with the bodies of dead children, but The Hunger Games really takes that to the next level and makes Katniss do the killing. Then, when the Capitol is defeated and things are supposed to be looking up, the leader who's supposed to be taking everybody to a bright happy future turns out to be a new version of the same old bad guy. So Katniss is forced to cross the line that no hero should ever cross.
3) Paul Atreides
Twenty years after the publication of Dune, Frank Herbert said, "The bottom line of the Dune trilogy is: beware of heroes. Much better rely on your own judgment, and your own mistakes." His point is amply made by Paul's journey, which basically maps onto Campbell's monomyth (but also includes things like setting himself up as a messiah and killing billions of people.) Indeed, Atreides may top this list in terms of number of people murdered, and it's a pretty competitive group.
4) The Doctor
He's not prophesied to become a hero, exactly, but he does follow the call to adventure -- running away from his home planet of Gallifrey in a stolen time machine and fighting evil on countless planets. And for most of his career, the Doctor follows some form of the hero's journey, even confronting his mentor gone bad (Borusa) and rejecting his own inner darkness in a few ways. He goes on quests and rights wrongs. Until the Time War -- when he nearly commits genocide on an unimaginable scale (a crime he actually spends hundreds of years believing he's committed.)
As one of the Slayers, Faith is quite literally the Chosen One, marked by prophecy to fight evil. She's the only one with the power to stop the vampires, demons and assorted other monsters from preying on the innocent. Until she goes off the rails -- and then she kills a human, which is a Slayer no-no. Soon enough, she's going to work for the evil Mayor of Sunnydale and helping him to become a scary principal-eating giant serpent. Later, Faith does find redemption, but her "hero's journey" has still gone on some very nasty twists by that point.
6) Harvey Dent
No matter what version of the Batman-mythos you follow, Harvey Dent always starts out as a hero. He's a crusading D.A. who tries to take down Gotham City's terrible crime families -- until he gets acid thrown in his face by Boss Maroni. Then, with half his face covered with scars, he becomes a monster, whose moral compass is entirely decided by a coin toss. Dent's journey from hero to evildoer is always tragic, but in Christopher Nolan's The Dark Knight he's set up as much more of a straightforward hero for the first half of the film. He's on the path to adventure, righting wrongs, until he falls off the path in a huge way.
As this livejournal post explains, Starbuck's story closely follows the hero's journey for most of the new Battlestar Galactica. She first refuses then follows the call to adventure -- and then she's given the Arrow of Apollo, which sends her on her path. A lot of the other steps on the Journey are checked off along Starbuck's route as well. And then... she apparently loses her mind and gets herself killed in a random explosion. She comes back, but apparently it's not really her because she eventually comes across her actual body in a raptor, and it's horribly burned. And an angel or something else has replaced her -- and whoever it is, she's really into loud piano-playing, heavy drinking, and bad choices.
8) Tony Stark
Iron Man doesn't really get the "call" to adventure as such -- he's put in a horrible situation where he has to improvise a suit of armour to get out of a cave where he's been trapped by a psychotic strongman. But once he's got that armour, he does become a hero and go on lots of classic hero adventures, in which he experiences lots of personal growth and sets the world to rights. But his path has a lot of strange twists in it, including his descent into alcoholism and self-destruction (and we won't even mention that time he turned out to be Kang's mind-puppet and was replaced with his own teenage self.) But it's really around the time of Civil War that the comics version of Tony Stark goes way off the hero's path and creates an evil cyborg clone of Thor, while also forcing a ton of other heroes into a prison in the Negative Zone. In the movies, meanwhile, he's responsible for creating Ultron among other problems.
9) Ender Wiggin
A foolproof plan for raising a well-adjusted child: take a six-year-old, subject him to super abusive schooling, ignore when he's being brutally bullied, when he kills the bully don't tell him, and finally trick him into committing genocide on a planetary scale. Ender's path may correspond to the hero's journey, but it's a particularly sick reflection of it.
10) John Connor
And finally... John Connor is about as classic a Campbellian hero as you can get. His birth is absolutely prophesied, and he's the saviour of the human race. He's prepared for years to lead the resistance against Skynet, and encounters lots of darkness and loses his mother (his mentor) along the way. But then, depending on which version of the Terminator saga you go with, he goes kinda wrong. In The Sarah Connor Chronicles, Future John becomes overly dependent on Terminators for advice and will no longer really talk to humans. In Terminator Salvation, he gets mortally injured and gets the heart of a Terminator. And in the new movie, Terminator Genisys, he... well, let's just say the trailers make it look like he's gone to a very, very bad place.