In the ever-changing drama of comics, there are stories where supervillains have taken over for superheroes. It's not always the cut-and-dried good versus evil format we've come to accept from so much superhero media, however. Some of these villains legitimately want to do good, not just mess up a superhero's reputation. Even the most tyrannical despots can become champions of virtue, often times seeking redemption from their criminal ways... well, at least temporarily.
Occasionally, there are villains who subbed for heroes that died or were incapacitated. Other times, there were superheroes and supervillains who switched places. Motivations vary. Some villains have a change of heart, others see an opportunity for redemption, and some villains are just trying to beat heroes at their own game. Check out this list of confirmed villains that shockingly tried to act as heroes.
In Dan Slott's celebrated Amazing Spider-Man run, Dr. Otto Octavius transferred his mind into the healthy body of his rival, Peter Parker, and switched Peter's mind into his own dying body. While Peter's mind was in the terminally ill shell of Doc Ock, Otto realized that not only did he have Spider-Man's body, but his memories as well.
All of the pain, love, and despair of Peter's past flooded into Otto's mind. Overwhelmed by Parker's strength and selflessness, Otto decided to not only take over the mantle of Spider-Man, but become The Superior Spider-Man.
The "superior" Spider-Man was less chatty and more ruthless, but he adequately filled the void Peter left behind. Over time, Peter's consciousness would return to his body and Octavius was ousted from his mind, returning things to normal.
#21 on The Best Comic Book Villainssee more on Dr. Otto Octavius
In the Infamous Iron Man series, Tony Stark is incapacitated. His absence paves the way for an unlikely self-appointed replacement: Victor von Doom. A calculating tyrant and merciless despot, Doom had a change of heart after the events of the Secret Wars crossover event.
Basically, he found that being a god wasn't as satisfying as he thought. Humbled and restored to mortal status, Doom embarked on a new path, trying to fill the scientific adventurer void that Tony Stark left behind.
Also Rankedsee more on Doctor Doom
The villainous Venom made a pact with Spider-Man to leave one another alone, under the condition that Venom no longer commits crimes. Well, if you are a superpowered symbiote and can't commit crimes, what's the next best thing? Fighting crime!
In Venom: Lethal Protector, Eddie Brock and the Venom symbiote travel from New York to San Francisco, taking out purse-snatchers and fighting evil along the way. This shocking turn would be temporary, but the Venom symbiote would find itself fighting for good once again years later when it merged with Flash Thompson, serving as both a Secret Avenger and a Guardian of the Galaxy.
Also Rankedsee more on Venom
At the end of the DC event Forever Evil, public opinion of Lex Luthor was at an all-time high after he helped to take out the dimension-invading Crime Syndicate. Taking advantage of this public approval, Luthor tried to convince the Justice League to recruit him. Because it's comic books, it worked! However, it should be noted that Luthor's enrollment into the Justice League was mostly to keep an eye on him, and to prevent him from committing any potential criminal activity.
Despite clashing with Superman and other members of the League, Luthor pulled his weight as a hero and served mankind, albeit without the noblest intentions. He even took over Superman's role as Metropolis's protector, weathering the general mistrust of the superhero community.
Also Rankedsee more on Lex Luthor