Redemption Failure

After undergoing an genuine Heel Face Turn (often after a "My God, What Have I Done?" experience), the formerly-evil but now honestly good character is forced by the circumstances (usually a great injustice done to him or the death of his loved one) to revert to his evil and violent ways again, losing everything good that he earned during his benevolent phase. A form of Tragic Monster.

The Moral of the Story being: Being Good Sucks but Being Evil Sucks even more and circumstances will conspire to tempt you from one to the other.

Compare Chronic Villainy, where the ex-baddie has an inner compulsion to commit evil again (rather than being forced into it by external circumstances); Reformed but Rejected, where everyone thinks that he will revert even though he does not; and Deadly Change-of-Heart, where an evil character wants to go clean but is not even allowed to start. Contrast Heel Face Revolving Door, where the bad guy changes alignment so often, it's hard to speak of any redemption in his case.

Anime and Manga

 * Roberta in Black Lagoon quits the Professional Killer business to become an simple maid, only to resort to massive violence again after her master is killed.
 * In Soul Eater this happens to  in the manga. In both the manga and the anime   In the anime  gets better. In the manga they
 * In Dragonball Z, Buu is convinced to stop his rampage by Mr. Satan/Hercule for a time, but his destructive nature breaks free and later takes control once entirely after a criminal shoots his pet puppy and wounds Mr. Satan.
 * Throughout the first half of Durarara!!, we see reference to the original leader of the Yellow Scarves abandoning the gang after a turf war went bad. Then, in part 2,  is revealed as that same original leader when he retakes control of the group to defend themselves from The Dollars and The Slasher. While he was never evil, per se, he treats it like an example of this.

Comic Books

 * Since he's something of an Expy of Clint Eastwood's characters, Saint of Killers in Preacher (Comic Book) gets a backstory about his life as a retired outlaw and gunslinger. Things rapidly go awry in fashion very similar to what befalls Eastwood's character in Unforgiven. See the Film section for more details.
 * In 52, the very Anti Heroic, if not outright villainous, Black Adam decides to start flying straight under the influence of his two new Morality Pets and turns his dominion Kahndaq into a rather utopian place. Then, Which he does, becoming the most wanted mass-murderer on the planet for a while.

Film

 * In American History X, some alternative endings have cause Derek to revert back to his old, racist ways.
 * William Munny in Unforgiven is a former badman, who tried to make a go at being a farmer. When his farm fails he decideds to take just one more job and for a time goes back to his old ways. (Although it's hinted at at the end that he eventually returned to a mundane life once more.)
 * The Godfather Part III has Michael's famous "Just when I thought I was out... they pull me back in."
 * The plot of Kill Bill plot is driven by this trope. The Bride faces a major Redemption Failure at the very beginning of the film: in the little chapel of Two Pines (Texas), the rehearsal of her wedding is ruined by former friends from her former assassin's life. . The last three and half hours of film depict her vengeance. A vengeance that feeds on what she wanted most to forget about: her mind-blowing killing-machine skills.

Literature

 * in The Dresden Files becomes a Vegetarian Vampire after nearly killing his love interest but reverts to a full-on vamp after being tortured and forced to lethally feed on humans by a resident Eldritch Abomination.

Live Action TV

 * In Justified, Boyd Crowder tries to go straight but circumstances keep pointing him back toward a life of crime.
 * Lindsey on Angel becomes a Heel Face Revolving Door as he abandons his evil employer but can't manage to not return, once it seems he finally has he comes back anyway plotting against Angel out of jealousy, after failing he agrees to team up with Angel again, but with the realization that he will turn on the team again when things go bad,

Video Games

 * Ray McCall in Call of Juarez is a criminal who became a priest but takes up his guns again when his other brother is murdered.
 * Hitman contains an Anti-Hero (or possibly Anti-Villain) example. In the second game, 47 abandons the life of crime to become a gardener for a priest, yet he's forced back into it when his employer is kidnapped..
 * In Red Dead Redemption, John Marston quits the life of an outlaw after his "friends" leave him to die, but The Government kidnaps his wife and son and orders him to dispose of his old comrades. He is forced to go back to his bad ways and although the player largely determines whether he becomes evil again, even with a good karma he still kills an awful lot of people on the way.

Western Animation

 * Harley Quinn in the Batman: The Animated Series episode "Harley's Holiday", though because it is Played for Laughs, this is a borderline Deadly Change-of-Heart example, too.