Warren Hamilton Lewis (16 June 1895 – 9 April 1973) was an Irish historian and officer in the British Army, best known as the elder brother of the author and professor C. S. Lewis. Warren Lewis was a supply officer with the Royal Army Service Corps of the British Army during and after the First World War. After retiring in 1932 to live with his brother in Oxford, he was one of the founding members of the "Inklings", an informal Oxford literary society. He wrote on French history, and served as his brother's secretary for the later years of C. S. Lewis's life.