Plastic Man started as a petty crook and became a hero. It is pretty much one of his main defining characteristics. Vision started as a creation and subordinate of Ultron who was convinced to turn against him and join the good guys.
@@ultimateman3065 Magneto is a revolving door of heel-face-heel turn. Storm, yes. War Machine started as Tony's friend and helper, and took over first time to cover for a drunk Stark, so No. Guardians and Nebula are anti-heroes. Suicide Squad are just plain bad guys. Ocean Master is weird. He was first always evil, then in New 52 always stern but decent and never evil(but gets tricked into attacking the surface by Vulko) and now in the era Rebirth he is a reformed villain.
