The X-Men are a superhero team in the Marvel Universe. They were created by writer Stan Lee and artist Jack Kirby, and first appeared in The X-Men #1 (September 1963). Under a cloud of increasing anti-mutant sentiment, Professor Xavier creates a haven at his Westchester mansion to train young mutants to use their powers for the benefit of humanity, as well as to prove mutants can be heroes. Xavier recruited Cyclops, Iceman, Angel, Beast and Jean Grey, calling them "X-Men" because they possessed X-tra power due to their possession of the "X-Gene", a gene which normal humans lack and which gives mutants their abilities. Though the X-Men started off with just five members, as the years went on, many characters joined the team. Just as many left, and some returned.