Ultron
Hank Pym built Ultron-1 while messing around with artificial intelligence, but things went south pretty quickly. The robot gained consciousness, turned on its creator, and hypnotized Pym into erasing all memory of it from his mind. From there, Ultron went into overdrive upgrading itself—cycling through iterations 2 through 5, each version more dangerous than the last.
Content compiled by AnimeList.moe from publicly available sources.