The X-Men are a team of fictional superhero characters in comic books published by Marvel Comics. The X-Men series has been adapted in various media, including animated television series, video games and a successful series of films.
The team's name is a reference to the "X factor", an unknown gene that causes mutant evolution. Co-creator Stan Lee recalled in his book Son of Origins of Marvel Comics that he devised the series' title after Marvel publisher Martin Goodman turned down the initial name which originally referred to "Xtra Powers", "The Mutants." In addition to this "official" explanation, the X-Men are widely regarded, within the Marvel Universe (as well as by the readers of the series), to have been named after Xavier himself. In Uncanny X-Men #309, Xavier claims that the name "X-Men" was never sought out to be a self-tribute. This lends credence to the statement Xavier made in Uncanny X-Men #1, in which Xavier stated he called the team X-Men "for ex-tra power!"