Wolverine played by Jim.
Wolverine (real name Logan) is a mutant with the ability to heal and regenerate from any amount of damage.
Jim is a rather gung-ho roleplayer, interested in action, cool fight scenes, and lucrative spoils over careful consideration or puzzle solving. He frequently acts before he thinks, which includes fixating on his own strange explanations for setting details that the GM hasn't explained yet.
Jean Grey is a mutant with psychic powers of telekinesis and telepathy.
Jean is played by an acquaintance of Ben's, who attends his drama classes. She was interested to come along and see what this "roleplaying games" thing was all about, after Ben described it to her as a sort of improvisational acting thing. She is dedicated to playing her character as a real, complex person with motivations inspired by a well-considered backstory.
Professor Charles Xavier played by Pete.
Professor Charles Xavier is the leader of the X-Men and founder of the Xavier Institute for Higher Learning.
Pete is an old friend of Jim's. Jim invited him along to join in this new game. Pete designed a character to maximise all the skills he thought would come in most useful in a superhero game, at the cost of being a bald, paraplegic, retirement age professor.
Cyclops played by Ben.
Cyclops (real name Scott Summers) is a mutant.
Ben is a thoughtful roleplayer who tries to think through the best course of action within his character concept and the setting. He enjoys coming up with clever ways to justify the success of his plans within the premises of the setting.
Storm played by Sally.
Storm (real name Ororo Munroe) is a mutant with the ability to control the weather.
Sally is Ben's younger sister. Ben took her along to the game on the first evening when his parents couldn't get a babysitter for the night. The GM quickly gave her a character to play so she wouldn't get bored. She enjoys the make-believe aspect of the game, but has some trouble separating it from reality.
Rogue (real name Marie) is a mutant with the ability to absorb other mutants' powers. She is 16 years old, and uses her great wisdom and popularity to play pranks on other mutants in Xavier's school. How exactly she gets away with this is a mystery.
Magneto (real name Erik Lehnsherr) is a mutant. His main concern is recovering the mystical Lost Orb of Phanastacoria, a powerful mutagenic artefact capable of turning non-mutants into mutants.
Mystique is a mutant with the ability to change shape into any human form. Magneto trusts her implicitly, but Toad suspects Mystique is up to some sort of nefarious plotting behind their leader to take absolute power into her own greedy hands. Who is right remains to be seen.
Toad is a mutant with a prehensile tongue and the ability to perform incredible athletic leaps. As such, part of his job is to keep Magneto out of trouble, which seems to be a very difficult thing to do with X-Men around.