The early 1960s were a busy time for Stan Lee of Marvel Comics. In November of 1961, he and Jack Kirby came up with The Fantastic Four, an answer to The Justice League, a comic that had been doing well for rival publisher DC. In March of 1963, The Amazing Spider-Man was given his own comic after an auspicious debut the previous fall. And then, in September of 1963, The X-Men appeared.

In that first issue, which is still the most collectible vintage X-Men comic available, the world was introduced to not just one new superhero but five—Angel, Beast, Cyclops, Iceman, and Marvel Girl. Also introduced in that first issue was Professor Xavier, the leader of the X-Men, and Magneto, the group’s arch-villain who, like them, is also a mutant with superpowers.

Besides issue number one, collectible vintage X-Men comics include issue four, which features the return of Magneto, issue 12, which focused on the origins of Professor Xavier and the introduction of Juggernaut, and Giant Size X-Men in the summer of 1975. That was the first X-Men comic to feature Wolverine, who had appeared in October of 1974 in Incredible Hulk issue 180. In 1975, the New X-Men was launched—that first issue, number 94, is also much sought-after.