Cosmo Hamilton (29 April 1870 in Norwood, England – 14 October 1942 in Guildford, England), born Henry Charles Hamilton Gibbs, was an English playwright and novelist. He took his mother's maiden name when he began to write. Hamilton was married twice: First to Beryl Faber, née Beryl Crossley Smith, the sister of C. Aubrey Smith who died in 1912, and then to Julia Bolton, the former wife of playwright Guy Bolton. He was the brother of writers A. Hamilton Gibbs and Sir Philip Gibbs. His London musicals include The Catch of the Season (1904), The Belle of Mayfair (1906), The Beauty of Bath (1906). He then wrote a number of Broadway shows, and many screenplays. Hamilton wrote dozens of novels, averaging a novel per year most of his adult life. His novels include: During the First World War Hamilton was a lieutenant in the Royal Naval Air Service.