During his tenure at Marvel, Claremont co-created numerous X-Men characters, such as Rogue, Psylocke, Shadowcat, Phoenix, The Brood, Lockheed, Shi’ar, Shi’ar Imperial Guard, Mystique, Destiny, Selene, Reverend William Stryker, Lady Mastermind, Emma Frost, Tessa, Siryn, Jubilee, Rachel Summers, Madelyne Pryor, Moira MacTaggert, Lilandra, Shadow King, Cannonball, Warpath, Mirage, Wolfsbane, Karma, Cypher, Sabretooth, Empath, Sebastian Shaw, Donald Pierce, Avalanche, Pyro, Legion, Nimrod, Gateway, Strong Guy, Proteus, Mister Sinister, Marauders, Purifiers, Captain Britain, Sunspot, Forge and Gambit.
Claremont scripted many classic stories, including “The Dark Phoenix Saga” and “Days of Future Past”, on which he collaborated with John Byrne. He developed the character of Wolverine into a fan favorite. X-Men #1, the 1991 spinoff series premiere that Claremont co-wrote with Jim Lee, remains the best-selling comic book of all time, according to Guinness World Records. In 2015, Claremont and his X-Men collaborator John Byrne were entered into the Will Eisner Award Hall of Fame.