The word fan somehow doesn't seem right for someone who starts reading C.S. Lewis and then somehow never stops. Follower? No. Devotee? Wrong. Admirer? Closer, but still not perfect, since Lewis was never about drawing attention to himself, but rather to Jesus Christ. So how about mere Christian? I like it.
What I found most interesting, for some reason, was the number of entryways into Lewis. Not surprisingly, Mere Christianity is mentioned most often as the book that people read first. Others tell about the influence of the Narnia books. The Screwtape Letters, the science fiction novels and works like Surprised by Joy, The Problem of Pain and Miracles. Yet there are others who cite Lewis's literary works, such as A Preface to "Paradise Lost" and Studies in Words, and essay collections like God in the Dock and The Weight of Glory. Lewis wrote so much and with so much variety, including poetry, with virtually everything still in print, that one can discover him through any one of many doors. And if you read one thing, you tend to seek out others.
I entered through the Mere Christianity door while in college, struck immediately by the strength of his intellect, his logic and his metaphors. Soon I was reading (and collecting) everything by or about Lewis I could get my hands on.
Some of the "mere Christians" included in the book are people you may have heard of, including Charles Colson of Watergate fame, geneticist Francis Collins, pollster George Gallup Jr. and writers like Liz Curtis Higgs, Anne Rice, Philip Yancey, Elton Trueblood and Clyde Kilby. Also included are Joy Davidman, the American poet who became so impressed with Lewis's books that she went to England to meet him and eventually married him, and Merrie Gresham, who married one of Davidman's son and Lewis's stepsons and only later became a mere Christian herself. It happened because she listened to a tape of Mere Christianity.