Clive Staples Lewis was a British novelist, poet, academic, medievalist, literary critic, essayist, lay theologian, broadcaster, lecturer, and Christian apologist. He held academic positions at both Oxford University and Cambridge University. He is best known for his works of fiction, especially The Screwtape Letters, The Chronicles of Narnia, and The Space Trilogy, and for his non-fiction Christian apologetics, such as Mere Christianity, Miracles, and The Problem of Pain