Gorilla Man, AKA Doctor Arthur Nagan, is a villain in the Marvel Universe, and an of Spider-Man's as well as the Defenders' enemy.
Doctor Arthur Nagan was once a brilliant surgeon and an even greater inventor. He invented an injection that would allow any part of any other life form to be replaced by a similar version of that life form. He thought about how the ape's body were superior to their human counterparts. So, Dr. Nagan He had his head transplanted onto the body of an abnormally large ape. He also started a group called; The Headmen.