Doctor Octopus got cancer. He was dying. So, being a supervillain, he schemed. He came up with a way to switch minds with Peter Parker, putting Peter’s mind in the dying body of Doc Ock, and assuming Peter’s life. The Octavius body died, taking Peter with it, and Otto kept the Parker body. But, instead of continuing his evil ways, he kept on being Spider-man, considering it his ultimate victory, but also being inspired by Peter’s memories. He would be the Spider-man the world truly deserved, the better Spider-man, the Superior Spider-man. Becoming more ruthless, even killing some of his enemies, he became more Dark Knight Returns Batman, even forming an army and building Spider-mechs.