Peter has the mutant power of turning his body into organic-steel, increasing his size and strength in that form. He was recruited by Charles Xavier into the X-Men during the Krakoa incident, and stayed in the states since then, although he firmly loves his country. He held a relationship with Kitty Pryde for a long time, but fell in love with a healer during the Secret Wars (Szaji, who died in those Wars) and broke with her. Since then, he hasn't involved with anybody else, feeling guilty for breaking Kitty's heart.

Peter used to be delicate, sensible and innocent, but since he lost all his family (parents killed by the government, brother killed himself after going mad, and sister victim to the legacy virus) he went cold and distant, and quite more wild than he used to be. He has been an artist till that moment, but he stopped painting and burned his pictures.

When Magneto invited him to join his acolytes, Peter accepted due to his pain and believing that that was the only way of dealing with violence : turning violent. The truth is that Colossus held his principles and after the lobotomization of Magneto by Xavier, he stayed in Avalon taking care of him and trying to spread Xavier's dream between the Acolytes.

Lately, he has joined Excalibur. It seems now that Mikhail is not dead but in another dimension (see Storm limited series).

The man known as Colossus has had a troubled past. Once one of Russia's premier heroes, he became disillusioned when his brother, Mikhail, became one of Apocalypse's Horsemen. When news of the atrocities that his brother was committing reached his ears, he travelled to America and offered his services to Magneto, whom he considered the leader of the premier band of mutants. Magneto quickly put both Colossus and Shadowcat in charge of training the next generation of X-Men to insure that the fight would continue if he or his X-Men were ever defeated by Apocalypse. When Magneto saw a chance to change the past, he instructed Colossus and his charges to find the one possible time-traveller that Apocalypse had not exterminated, still within the slave pits: Illyana Rasputin.

Colossus has currently rejoined the X-Men and is searching for Xavier with them.