Favorite character that goes from being a villain to a hero?
Two-Face (DC Comics): Has gone from a hero to villain and back to hero in more recent media, such as his current miniseries and the Caped Crusader series on Amazon Prime.
Harley Quinn (DC Comics): Taken a similar route to Two-Face as of late, with a big example being the Harley Quinn show.
Crowley (Supernatural): Starts off as King of the Crossroads, bargaining souls with the people who own them and with other demons, to eventually sacrificing himself to save the world.
Leonardo Snart/ Captain Cold (DC Comics): The biggest example of this is in the Legends of Tomorrow show on CW, in which he briefly joins the fight to save the world, after having previously been basically just a petty robber and thief who just so happens to have a gun that freezes things.
Kite-Man (DC Comics): I could be wrong here, but I do believe he’s been an antihero recently.
Poison Ivy (DC Comics): There appear to be a lot of DC examples to this. In the Arkham Knight game, she uses the last of her lifeforce and willpower to save Gotham from Scarecrow’s fear toxin (her life would’ve been spared, had Batman called the Justice League, but I digress).
Luci (Disenchantment): Originally meant to be the devil on the shoulder of the princess, he eventually sacrifices his life to save her, and winds up in Heaven.
Omni-Man (Invincible): After killing the Guardians of the Globe, he heads to space to rethink some things, before helping his son find the weaknesses to the Viltrumites. He also eventually sacrifices his life for the greater good.
Weasel (DCU): Apparently never having been a villain in the first place, Weasel goes from being imprisoned for eating children, to helping stop another World War/ genocide (even if unintentional).
Bloodsport (DCU): Went from an assassin, to saving a foreign country from a giant alien starfish.
Wolverine (Marvel Comics): Originally a Hulk villain, he eventually became a hero and leader of the X-Men, dedicating his life to doing good.
Deadshot (DC Comics): Often a member of the Suicide Squad, he often risks his life to help save the world, so he gets a reduced prison sentence, so he gets to chance to hopefully see his daughter again, and make a better life for her.
Loki Laufeyson (MCU): Went from one of Thanos’ cronies, to dedicating the remainder of his life to protecting all life throughout the multiverse.
Megamind (Megamind): Went from being the supervillain, to being the superhero. He spent his life hating Metroman, but once Metroman was gone, he realized he lived for the thrill of the fight, not the satisfaction of the victory. So he created a new hero, who became a villain, so he became a hero to fight the new villain, and also so he could get the girl he wanted.
Gizmo (Suicide Squad: Kill the Justice League): I’m grouping him with the rest of the Suicide Squad, in the sense that they’re risking their lives to save the world (even if it’s for selfish reasons).
Negan (the Walking Dead): Went from killing two fan-favorites, to throwing himself in harms way to save several other characters.
Arthur Morgan (Red Dead Redemption II): Lived his life as an outlaw, but spent his last few months trying to remedy many of the wrongs he’d done.
The Ghoul (Fallout): Was a bounty hunter, until he began hunting down Hank to get his revenge for dropping the bombs on America.
Rowena (Supernatural): One of the most powerful witches, who only cared about herself and her own personal gain, until she started working with the Winchester brothers, and began changing for the better, eventually apologizing to her son, whom she had mistreated for all his life.
Meg Masters (Supernatural): Went from a demon who wanted to take over the world, to sacrificing herself to save the world against a greater evil