Simon Says was a Teen GeniusMad Scientist outcast who became a supervillain due to being bullied by the jocks at school. However, the death of local superhero Starbright, which revealed that he had been a jock that had tried to help Simon when they were younger, causes Simon to reassess things, use Starbright's technology to transition into being a woman (the cause for the bullying against her), and eventually take up Starbright's mantle as a superhero.
Steeljack was a small-time villain who eventually realized that his career was essentially pointless. Even when he did make the big score, it never made any difference. After making parole for the final time, he decides to try and improve things in the slum he grew up in, where he becomes an all-around go-to guy if you're having problems, and the caretaker for the local cemetery where his mother was buried. He also ends up inspiring the second Goldenglove to become a hero rather than a criminal like her father. He doesn't consider himself a "hero," exactly, but his actions show him to be a good and decent man.
In "Nightmare Life", the Living Nightmare develops a sense of self, overcoming the pain that its various masters used to control it and deciding to become a hero.
Andy Merton was a petty criminal who happened to steal the magic amulet that had belonged to Stormhawk. He accidentally triggered it, merging with his corgi and gaining superpowers. He also gained a strong empathic link to the dog, whose sense of loyalty and herd instinct steered him away from crime and toward using his new powers to help people as a hero.
In the original English language manga Amazing Agent Luna, Timothy Hyatt, upon learning Elizabeth Westbrook is to be killed, switches sides and helps her escape. He later returns to deal with his former partner, Martin Williams.
The demons of Clean Room are universally evil, but one was turned from its nature by an unusually successful exorcism.
Also, the demons recruited a human banker to secure financial records in exchange for a cut of their profits. After fulfilling his end, the banker learned the truth of their aims and rebelled. It didn't work out for him.
Clem Hetherington: In the first book, "Clem Hetherington and the Ironwood Race", Brecht Ironwood had an epiphany after spending ten years as a tomb robber. From that point on, he dedicated his life to tracking down the artifacts he stole and sold on the black market to return them to the tombs they came from.
Garganta from Femforce debuted as a villain. Popular with readers, she was brought back as a recurring character, with her original rampage being revealed as a side-effect of the experiment that gave her her powers. She eventually became an auxiliary member of Femforce.
Hellboy is one of the most glaring examples. From birth, he was destined to usher in the apocalypse under the name Anung Un Rama as The Antichrist. Instead, he wants nothing to do with it and becomes an Anti Anti Christ, going as far as to keep his demon horns filed down.
Hybrid Force: Octo, Thorn, and Lizard Lady start the comic as members of the terrorist organization Testify. While on a mission, they suddenly regain their lost memories and turn against the group. They then decide to track down their old lives and put an end to Testify's plans.
Powerplex in Invincible always considered himself a hero in his single-minded obsession with killing Invincible — but after Invincible left the planet for an extended period, he received counseling and a second chance as a member of the superhero team the Actioneers. However, when Invincible returned, he couldn't control himself and attacked him again. After finally accepting the fact that Invincible wasn't at fault for his sister's death and that the death of his wife and son were on his shoulders and his alone, Powerplex surrendered. In a later conversation with Cecil, Invincible learns that Powerplex was a real hero while he was away, and will be again after more counseling.
In the Irredeemable spinoff Incorruptible, former supervillain Max Damage realizes that The Plutonian'sFace–Heel Turn will now leave the general public without a true Big Good to defend them. In response, he decides that he needs to step up for the people and tries hard to be a hero.
In the Madballs comic book published by Star Comics (a subsidiary of Marvel Comics that is now defunct), the second series Madballs and the Super Madballs were initially created by Dr. Viktor Frankenbeans to be Evil Counterparts to the original Madballs, but they ended up turning against the doctor and siding with the original Madballs.
King Sombra does so the end of "The Siege of the Crystal Empire" arc in the My Little Pony: Friendship Is Magic (IDW) comics, after realizing he's become the monster he saw in the Crystal Heart from a thousand years prior.
The Powerpuff Girls: Mojo Jojo attempts a Heel-Face Turn in the comic story "Monkey Business". He opens a restaurant which is a hit with the patrons. However, the girls are still quite suspicious and uncover what they think is criminal activity. They are proven wrong each time, but it's the last act that makes Mojo give up his restaurant business and return to a life of crime.
As well, Shadow and Rouge did their own Heel-Face Turns, though Rouge was always on that border. For Shadow, it was finally getting tired of not knowing who he was that provoked the turn.
The Transformers comics have a number of Decepticons leave the cause, in part due to the Adaptational Heroism the faction has had, and also due to the truly wretched participants in the group.
Thundercracker leaves the Decepticons in The Transformers: All Hail Megatron, after the slaughter of thousands of humans as well as the conversion of almost three thousand of their own men into monsters due to the Decepticon experiments.
After the events of AHM, Dirge leaves the Decepticons after they abandon him, and he and Swindle aid the neutrals and Autobots during the post-war upraising in The Transformers: Robots in Disguise. Similarly, Tankor and Squawkbox depart from the Cons as well as they felt the peace achieved with Megatron's defeat was preferable to the fighting (Tankor himself went on to be a supporting cast member in the The Transformers: Windblade series).
Ambulon became an Autobot after the Decepticons forcibly entered him into their (failed) combiner program, leaving him with the useless alt-mode of a leg in The Transformers: More than Meets the Eye. In season 2 Ravage joins the Lost Light crew to stay by Megatron's side both out of loyalty and seeing the massacre inflicted by the more zealous members of their side.
The Scavengers start out as a pack of corpse-looting petty thieves with some pretty nasty anti-organic bigotry. They grow out of it, eventually deciding to find traumatised post-war ex-Decepticons and help them recover.
Crankcase: What you're describing sounds suspiciously like helping people. Krok: I know, because guess what? I think we'd be pretty good at it.
In Violine, the doctor after being declared the world champion of the Pygmies. Van Beursen, Muller and Marushka later have amnesia-induced ones.
