How did C.S. Lewis convert from atheism to Christianity?

C.S. Lewis, an Irish-born scholar and author, converted from atheism to Christianity in 1931. He had rejected Christianity in his early teens and remained an atheist through his twenties. His spiritual and intellectual journey led him to theism in 1930, followed by his acceptance of Christianity the next year. This transformation was partly influenced by his close friend, J.R.R. Tolkien, a devout Roman Catholic. Lewis described these experiences in his autobiography, Surprised by Joy.1