Calvin Rankin was thought to have accidentally given mimicking abilities while looking around in his father's lab. While in reality, he was born a mutant, Homo superior. He quickly put his abilities to use excelling in school and sports, and began to become hotheaded because of it.
Eventually he became a temporary leader of their team, and over the years that followed, flip-flopped between teams (both official and criminal) like Excalibur and the Brotherhood of Mutants. Norman Osborn found use for his abilities and recruited him for a team of X-Men.