5. Xemnu
Originating from an unknown alien planet, Xemnu's first appearance in comics was when he crash-landed on Earth after having been one of several inmates on an "exile world". He snuck past several guards and onto a supply ship. The hijacked craft was only capable of bearing him half of the way home, however, and he ended up on this planet. He was found in Blacktree Swamp by an electrician named Joe Harper who tried to revive Xemnu by repairing his cybernetic parts in his workshop. There he revived Xemnu through an electrolysis process. While recharging, Xemnu revealed that he was a convict and then used his hypnosis rays to take control of Harper. After confirming that his hypnosis worked on humans, Xemnu brought Harper out of his trance and revealed his plan to enthral all of humanity. From thereon in, he encountered the likes of the Hulk, who proved immune to his mind-powers by virtue of his rage-filled mind, but Xemnu was still formidable enough in a physical sense to prove a worthy adversary for the big green hero. He posed enough of a threat to the Hulk for him to have to ask Doctor Strange for his help. In that regard, not only would Xemnu be an incredibly original and surprising Hulk villain in the Marvel Cinematic Universe, but he could also be an entry route for Doctor Strange. All things considered, Xemnu would be a most welcome and extremely non-obvious addition to the MCU.