When was M debuted in X-Men?
X-Men
September 1963
The X-Men are a team of fictional superheroes appearing in American comic books published by Marvel Comics. Created by writer Stan Lee and artist/co-writer Jack Kirby, the characters first appeared in The X-Men #1 (September 1963). They are among the most recognizable and successful intellectual properties of Marvel Comics, appearing in numerous books, television shows, films, and video games.