Kowalski became the main antagonist of Bruno Sammartino in the World Wide Wrestling Federation in the 1960's and 1970's. Kowalski formed a tag team with fellow heel Gorilla Monsoon and took Red Berry as his manager; Monsoon and Kowalski held the WWWF United States Tag Team Championship, winning the belts in two straight falls from Skull Murphy and Brute Bernard on Washington, D.C. television, and later losing to The Tolos Brothers in two straight falls in Teaneck, New Jersey in December 1963. On May 11, 1976, Kowalski won the WWF World Tag Team Championship with Big John Studd. Both men wore black masks and tights and called themselves "The Executioners". However, they were stripped of the championship, following the interference of a third Executioner during a title defense against Chief Jay Strongbow and Billy White Wolf. The Executioners lost a match for the vacant title on December 6 to Strongbow and White Wolf and never regained the championship. In 1977, Kowalski retired and left the WWF.
In 1996, Kowalski was inducted into the WWF Hall of Fame.
Kowalski passed away on August 30, 2008.