Calvin is not a born mutant. Early on in his life he inhaled an unkown chemical at his father's laboratory and he acquired the ability to copy features and abilities of any other person. This makes him a handy person indeed, except that he could only retain those feature as long as he was in direct vicinity of said person.

Mimic was first the X-Men's enemy. Later he was reluctantly accepted into the X-Men. But, of course, he was thrown out for over arrogance. Mimic is sometimes a hero, sometimes a villain. He has also had stints as a member of the British team Excalibur, and the Brotherhood of Evil Mutants. But his career, for all his vanity, has not really been that interesting.