"Alan Caillou was the nom de plume of Alan Samuel Lyle-Smythe M.B.E., M.C. (9 November 1914 – 1 October 2006), an English born author, actor, screenwriter, soldier, policeman and professional hunter. Alan Lyle-Smythe was born in Surrey, England. Prior to World War II he served with the Palestine Police from 1936 to 1939, where he learned the Arabic language. He was awarded an MBE in June 1938. He married Aliza Sverdova in 1939, then studied acting from 1939–1941. In January 1940, Lyle-Smythe was commissioned in the Royal Army Service Corps. Due to his linguistic skills, he transferred to the Intelligence Corps and served in the Western Desert where he used the surname "Caillou" (the French word for 'stone') as an alias. He was captured in North Africa, imprisoned and threatened with execution in Italy, then escaped to join the British forces at Salerno.
Much more about the Man From UNCLE in the Open Channel D book: