10 Most Interesting X-Men You've Never Heard Of
4. Mimic
For the first few years of their existence, Professor X's X-Men was purely composed of its original five members, Cyclops, Beast, Iceman, Angel and Marvel Girl (Jean Grey). Three years after the team began, Mimic was their first recruit.
Calvin Rankin was not actually a mutant. Instead, a serum gave him the power to copy the abilities of anyone around him. Initially he joined the X-Men in an attempt to gain their powers, but later became a hero for real when he seemingly sacrificed himself to stop the Hulk.
Mimic was actually only comatose though and would later return, first as a villain but later as an ally to the X-Men's British spin-off Excalibur.
Mimic sort of became an X-Man again when he joined Norman Osborn's Dark X-Men (hint: if you're on the "dark" version of your team, something's probably gone wrong). There he revealed that his earlier erratic behaviour was due to undiagnosed bipolar disorder and befriended teammate Weapon Omega, an energy manipulator.
Mimic later came to the real X-Men when Omega's powers went out of control. The X-Men were unable to help him though and so did what they always do with problems, put Omega in cryogenic suspension and immediately forgot he existed. Mimic took a teaching position at the Jean Grey Institue to remain close to his friend.