Completing his studies, he chose a career which took him to Oxford and the world of medieval literature. Not content with fantastic tales of the past, he became close friends with one of the greatest storytellers of his time: J.R.R. Tolkien (author of Lord of the Rings). And he closely studied George MacDonald (author of Phantastes).
Interrupted briefly by service in WWI (where he was injured at the front), Lewis returned to Oxford and became a tutor at Magdalen (pronounced MAWD-lin) College, where he remained for 29 years. He took part in brisk discussions about faith (or his lack thereof).
You must picture me alone in that room in Magdalen, night after night feeling, whenever my mind lifted even for a second from my work, the steady, unrelenting approach of Him whom I so earnestly desired not to meet.
That which I greatly feared had at last come upon me. In the Trinity Term of 1929 I gave in, and admitted that God was God, and knelt and prayed: perhaps, that night, the most dejected and reluctant convert in all of England.
C. S. Lewis Surprised by Joy