C.S. Lewis returned to Christianity in 1931, after a long period in which he considered himself an atheist.
His conversion developed through conversations with writers and scholars including J.R.R. Tolkien and Hugo Dyson. Lewis later described his movement toward belief in books such as Surprised by Joy and Mere Christianity, though different passages emphasize different stages of the process.
Lewis had been raised in the Church of Ireland but rejected Christianity during his adolescence. His return was gradual: he first became convinced of theism, then of Christianity. He became one of the most prominent Christian apologists in the English-speaking world.
A common oversimplification is to treat his conversion as a single sudden event. Lewis himself presented it as a progression, with important changes in 1929 and 1931. The year 1931 is conventionally associated with his return to Christian belief.