Willy Armitage was a professional weightlifter and an IMF member.
His dosser stated that he had set records as a weightlifter. Missions often called for him to lift heavy objects and make the act look easy, such as when he'd smuggle a fellow agent in a suitcase. In addition to heavy lifting, he was a skilled unarmed combatant; in one episode, he devised a blood choke that rendered a full grown man unconscious within seconds of application.
Willy participated even in missions that did not require brute strength, most often as a driver. Other episodes depicted him displaying skill in such things as painting, modifying and repairing automobiles, operating television broadcast equipment, electrician work, etc.
Peter Lupus portrayed Armitage throughout the original series run. His name appeared in the cast in every season. He was absent from the credits of a handful of episodes of Season 5, as the producers had made a short-lived attempt to replace Willy with Doug Robert (Sam Elliott). When the producers received an abundance of fan mail for Willy, they reversed this decision.
Of the main cast of the first three seasons, only Willy was never once shown smoking, as Lupus was the only nonsmoker of the cast.