Personality: Piotr is a good person, through and through. He is unshakably loyal to his team-mates and friends, and an unrelenting foe to anyone who would harm them. He is very proud of his Russian heritage, occasionally feeling guilt for having left his Mother Country behind.

Other distinguishing features: Peter is an very tall man with an exceptional physique. Think Arnie on mega-steroids.

Strength level: In his normal human form Peter Rasputin possesses the normal human strength of a man of his age, height, and build who engages in intensive regular exercise, (bearing in mind that he is of well over average height and build, this means that he is remarkably strong, capable of lifting 500-600 lbs). As Colossus he can lift (press) at least 70 tons under optimal conditions.

Fighting Skills: Colossus, as a member of the X-Men, has had extensive combat training, and is a skilled combatant, making full use of his size and strength in his combat maneuvers.

Special Skills and Abilities: Colossus is a skilled pilot, mechanic, and acomplished artist, as well as having developed alongside Wolverine, the practically unprecedented ability to hurl a team-mate into combat, with astonishing accuracy.

Known superhuman powers: Colossus is a mutant with the superhuman ability to convert the tissue of his entire body into an organic steel-like substance, granting him superhuman strength and a high degree of resistance to bodily harm. This substance, resembling organic steel, is of unknown composition but appears to be analogous to osmium and to carbon steel. He is able to transform into this armor-like state at will (the process is virtually instantaneous) and remain in that form for an as yet undetermined amount of time. (The longest time he has remained in armored form so far has been five days). Once in his armored form he remains so until he consciously wills himself back to normal. If he is rendered unconscious, however, he spontaneously reverts to his normal form. While in his armored state, Colossus possesses the same degree of mobility that he does in his normal form.

The process by which Colossus transforms himself to armored form and back (including his gain of additional mass from an unknown, perhaps extra-dimensional, force) remains unknown. Colossus cannot become partially or selectively armored; his body is either entirely converted or not. Even his eyes become steel-like; his eyeballs can withstand and deflect the impact of a .45 caliber bullet.

In his armored form Colossus is highly resistant to most forms of bodily harm. His armor is capable of withstanding ballistic penetration, including that of a 110 millimeter Howitzer shell. He could survive a collision with a loaded, one-ton flatbed truck at 100 miles per hour or an explosion of 450 pounds of TNT. He can survive extremes of temperature from 70 degrees above absolute zero (-390 degrees Fahrenheit) to approximately 9000 Fahrenheit. However, it is theorized that above the latter temperature, his armored form would begin to melt. Colossus's armored form cannot rust under normal Earth conditions.

Colossus is in unusually fine physical health, permitting the transition back and forth from his normal organic flesh state to his armored form to occur with minimal stress on his system. His normal lungs are capable of holding his breath for 3.6 minutes. In the past he has exhibited a minimal or nonexistent need to breathe while in his armored state. However, it is believed that he could not survive for long in a vacuum. His endurance and speed are somewhat greater in his armored form.

However, Rasputin was contacted by Professor Charles Xavier, founder of the X-Men, when Xavier was organizing a new team of mutant X-Men to help him rescue the original X-Men from the sentient island Krakoa. Rasputin agreed to leave the farm community in which he was born and raised to go to America with Xavier. Xavier gave Rasputin the code name "Colossus" and Rasputin aided Xavier's other new recruits in their battle against Krakoa. After the battle was won, Rasputin remained in the United States with the new X-Men while the rest of his family stayed on the farm.

Rasputin's family always remained in his thoughts. Shortly thereafter a woman known as Miss Locke kidnapped many of the X-Men's loved ones to use as hostages in order to force the X-Men to aid her in freeing her employer, Arcade, from captivity by one of Doctor Doom's robots. Among her captives was Colossus's younger sister Illyana, whom Locke had somehow kidnapped from the Siberian collective farm and transported to the United States. The X-Men freed Illyana from captivity, and she went to live with her brother Piotr (known as Peter in America) at Xavier's mansion. Due to her later captivity in a dimension known as Limbo where she spent years while only mere moments elapsed on Earth, Illyana became the adolescent sorceress known as Magik.

Later, Illyana became the first tragic victim to be infected with the Legacy Virus and die from it. The deaths of his immediate family caused Colossus to rethink his position with the X-Men a nd join Magneto and the Brotherhood, who had offered him an alternative to the X-Men's way of fighting and living.

His stay with Magneto was not long once he realized that Avalon was not the place for him, either. After some time alone, he eventually returned to the manions, realising it was the best place for him to be, and where he could best honour his sister's memory.