American actor best known for a short string of Hopalong Cassidy Westerns in the 1940s in which he played Cassidy's youthful sidekick Johnny Travers. Kirby was born William B. George in Missouri. He began acting in films in 1942 when he was cast to replace Russell Hayden in the Cassidy films. He served briefly as an aviation cadet in the U.S. Army Air Forces during the Second World War, though his screen appearances remained continuous throughout the war and afterward for several years. In 1949, he reverted, more or less, to his real name, Bill George, for the rest of his career. He left acting in 1957 and died at 44. He was buried in the Los Angeles National Cemetery.