Donald O'Connor (1925 -- 2003)
Born in Chicago into a circus family, O'Connor started performing acrobatics in vaudeville as a young child. In his teens he made his film debut, appearing as Bing Crosby's younger brother in the amiable family musical, Sing You Sinners (1938), then as Huckleberry Finn in Tom Sawyer, Detective (1939). More scripts flowed swiftly: in the 1940s alone he appeared in no fewer than 19 films. At the height of his powers as a light comedian, he was cast as Cosmo Brown in Singin' in the Rain (1952), directed by Stanley Donen and co-star Gene Kelly, which included a scintillating song & dance performance of Make 'em Laugh.
O'Connor remained busy throughout the Fifties, but his star began to wane as the golden age of movie musicals passed. He died aged 78 at a retirement home near Los Angeles.