Cosmo Charles Gordon-Lennox (17 August 1868 – 31 July 1921), whose stage name was Cosmo Stuart, was a British actor and playwright of the late 19th and early 20th centuries. He became known as an actor in the 1890s, but by the turn of the century he had begun to concentrate on writing, usually under his real name. He specialised in adapting French comedies for the British stage, but also wrote original works, often as vehicles for his wife, the actress Marie Tempest.