Colossus is a mutant that has the ability to transform his entire body into a form of "organic steel", with properties similar to osmium but of still unknown composition. Colossus must transform his entire body into this armored state; he cannot transform only a portion of his body. When he transforms, he gains around a foot in height and his weight is at least doubled. In his armored form, Colossus possesses superhuman levels of strength, as well as superhuman stamina and durability. His physical strength is currently greater than when he first joined the X-Men due to the realignment of his cells by Magneto following an injury during the Mutant Massacre. While in his armored form, Colossus requires no food, water, or even oxygen to sustain himself, and is extremely resistant to injury. He is capable of withstanding great impacts, large caliber bullets, falling from tremendous heights, electricity, and certain magical attacks. While he has great resistance to temperature extremes of hot and cold, extreme heat followed by rapid super-cooling has been shown to cause extreme damage. As he is vulnerable to the anti-metal vibranium in his metal form, his body instinctively shifts to human form when faced with a vibranium weapon.
Colossus is an excellent hand-to-hand combatant, having received training from Wolverine and Cyclops. He has had training in acrobatics and sword fighting from Nightcrawler. In his human form, he is exceptionally strong and fit, though not superhumanly so. He has completed college-level courses at Xavier's school.
Piotr "Peter" Rasputin was the child of Russian farmers, born with big shoulders and strong spirit. When his mutant powers emerged, his body become encased in living steel and he became one of the mightiest heroes of the Marvel Universe. Peter moved to America to join the X-Men, serving as both the heat and conscience of the team.