There are several prominent examples of comic book superheroes either temporarily or permanently turning to villainy and evildoing, including Marvel's Loki, Two-Face of the "Batman" comics, Mystique of "X-Men," Bucky the Winter Soldier of "Captain America" and Ozymandias of "Watchmen." Heroes are depicted as turning to a dark side, a life of crime or other evildoing for a variety of reasons; in "Star Wars," Darth Vader, who was born as a Jedi named Anakin Skywalker, is seduced and voluntarily turns toward evil, while in "X-Men," Jean Grey is accidentally exposed to an external force that changes her nature, after which she becomes the evil Dark Phoenix.
In most cases, a good character turning bad, or a bad character being revealed to have once been good, is a plot point in and of itself, offering a compelling narrative twist for readers and viewers. Some hero sidekick characters and even hero main characters have succumbed to the forces of evil. For example, Captain America's friend Bucky Barnes becomes the evil Winter Soldier, and Hal Jordan, the Green Lantern, becomes the villain known as Parallax. Sometimes, these characters are eventually redeemed or are shown to be evil in an alternate-reality timeline. In other cases, the character's change is a permanent one.