William Joseph Patrick O'Brien (November 11, 1899 – October 15, 1983) was an American film actor with more than 100 screen credits. Of Irish descent, he often played Irish and Irish-American characters and was referred to as "Hollywood's Irishman in Residence" in the press. One of the best-known screen actors of the 1930s and 1940s, he played priests, cops, military figures, pilots, and reporters. He is especially well-remembered for his roles in Knute Rockne, All American (1940), Angels with Dirty Faces (1938), and Some Like It Hot (1959). He was frequently paired onscreen with Hollywood legend James Cagney. O'Brien also appeared on stage and television.