"Singin' in the Rain" was by far Mr. O'Connor's most famous credit, a soaring MGM "A" musical in a career filled with "B" movie credits. Many critics consider his slapstick masterpiece "Make 'Em Laugh" the highlight of the film and one of the most sublimely perfect moments in movie musical history. In the number, Mr. O'Connor wrestles with a mannequin, flips off walls and walks in circles while flat on the floor, every moment exactingly, yet seemingly spontaneously, choreographed. A gangly man with big ears, a big grin and a rubber face, Mr. O'Connor often played likeable, quick-witted, though often befuddled juveniles. In the early '50s, he starred opposite Francis the Talking Mule in the popular film series featuring that animal.

On Broadway, he was Cap'n Andy in the 1983 revival of Show Boat. Two years earlier, he was in the very short-lived Bring Back Birdie.

Mr. O'Connor learned his trade in vaudeville from an early age. He was born Aug. 28, 1925, in Chicago, to John Edward O'Connor and Effie Irene O'Connor, both circus performers and dancers. His father died when he was six months old, and he soon joined his mother's act. He eventually danced in an act with his two brothers. Mr. O'Connor began acting in films in 1938.

Other movie musical roles included "I Love Melvin" and "Yes, Sir, That's My Baby."