In 1967, Perras became "The Russian Bear" Ivan Koloff, a bearded villainous character billed from Ukraine, and debuted with the International Wrestling Association in Montreal, Québec. He defeated Johnny Rougeau for the IWA International Heavyweight Championship the following year. Koloff debuted in the World Wide Wrestling Federation in late 1969, managed by "Captain" Lou Albano. He soon started a rivalry with then-WWWF World Heavyweight Champion Bruno Sammartino. On January 18, 1971, Koloff defeated Sammartino in Madison Square Garden for the WWWF World Heavyweight Championship by pinfall after a knee drop from the top rope, ending Sammartino's seven and two-thirds years reign. Koloff lost the championship 21 days later to Pedro Morales, essentially being used as a "transitional champion" (as he was used to move the title from Sammartino to Morales without having the two fan favorites work against each other), much like Stan Stasiak and The Iron Sheik would be in later years. After the loss, Koloff remained a contender for the title but never reclaimed it, leaving the WWWF in 1971.