Piotr Nikolaievitch Rasputin aka Peter Rasputin was born a farm boy and grew up with his brother Mikhail and sister Illyana - both also mutants - on a Soviet Collective Farm. Peter’s mutant abilities first manifested at the age of 13, and his good and humane nature aided his intent to only use his abilities to protect his family. It stayed that way, until he was discovered by Professor X.
Peter’s first involvement with the X-Men was when he was contacted and recruited by Charles Xavier (Professor X), in the Professor’s attempt to draft a new team of X-Men, in a desperate effort to save the original X-Men - Cyclops, Jean Grey, Angel, Havoc, Iceman, and Polaris - who were trapped on the island of Krakoa, the Living Island. This team was the second to be sent after Moira McTaggart’s band of young mutants failed to complete the mission, resulting in the death of two of the mutant members. They did however manage to bring Cyclops back to the professor.
With Peter’s newly established team of Nightcrawler, Storm, Wolverine, Bandshee, Thunderbird, Sunfire, and himself, the (new) X-Men set off for the island under the guidance of Charles. After a series of battles against the enemy, the new and old X-Men combined their abilities to eventually defeat Krakoa, and successfully returned as a group of 13 X-Men to Professor X’s mansion.
After the episode of Krakoa, Peter chose to remain in the United States with the X-Men while his family stayed on at the farm. His decision to become an official X-Man was acknowledged by being accorded the name Colossus.