8. Apocalypse
Just look at how awesome Apocalypse looks. He is one of the X-Men's most regular, long-standing, intimidating and mighty foes. He has such a vast and eventful history that an origin story would be absolutely fantastic as a movie. He was born in Jordan 5000 years ago and was abandoned as an infant due to his unnatural appearance. He was originally named En Sabah Nur by Baal of the Sandstormers, who rescued him and brought him up with the intention of utilising his powers, but would later become Apocalypse when his powers fully emerged due to the rage produced when Baal was killed. He is a genius mutant who has vast psionic powers and possesses other abilities such as technopathy, superhuman strength, molecular manipulation and energy manipulation. All of these powers and abilities are augmented by advanced Celestial technology, which makes him a truly formidable opponent and villain. He is a huge threat on several levels, in that he has the physical power to battle the likes of the Hulk, the mental power to battle the likes of Professor X and the intelligence to prepare plans and invent technology to make him a danger to almost anyone. There have been no characters like him in the X-Men movies up to now. His appearance is monstrous and would no doubt require CGI to pull off. However, there's no doubting that he would look incredibly cool on the big screen and could quite easily carry his own movie, given his interesting history and uncanny powers.