Clive Staples Lewis (November 29, 1898 – November 22, 1963), commonly referred to as C. S. Lewis, was an Irish author and scholar, born into a Protestant family in Belfast, though mostly resident in England. Lewis is known for his work on medieval literature and for his Christian apologetics and fiction, especially the children's series entitled The Chronicles of Narnia.

Career as a writer on Christianity
In addition to his career as an English Professor, and his novels, Lewis also wrote a number of books about Christianity — perhaps most famously, Mere Christianity which is considered a classic work in the area of Christian apologetics. After some years as an atheist, he converted to Christianity and joined the Church of England. Although he became an Anglican, he stated that he was influenced by his Roman Catholic friend Tolkien. He was very much interested in presenting a reasonable case for the truth of Christianity. Mere Christianity, The Problem of Pain, and Miracles were all concerned, to one degree or another, with refuting popular objections to Christianity.

He has become popularly known as The Apostle to the Sceptics, because he originally approached religious belief as a sceptic, and he was converted by the evidence. Consequently, his books on Christianity examine common difficulties in accepting Christianity, such as "How could a good God allow pain to exist in the world", which he examined in detail in his work The Problem of Pain.

Lewis wrote an autobiography entitled Surprised by Joy, which describes his conversion. (It was written before he met his wife, Joy Gresham.) His essays and public speeches on Christian belief, many of which were collected in God in the Dock and The Weight of Glory and Other Addresses, remain popular today for their insights into faith.

His most famous works, the Chronicles of Narnia, contain many strong Christian messages. These are often mistaken for allegory, but, as Lewis himself said, are certainly not allegory.

Trilemma
The term "trilemma" actually comes from Christian apologist Josh McDowell, who based it on one of Lewis's best-known arguments in favor of Christianity from his book Mere Christianity.

According to the argument, most people are willing to accept Jesus Christ as a great moral teacher, but the Gospels record that Jesus made many claims to divinity, either explicitly ("I and the Father are one") or implicitly, by assuming authority only God had ("The Son of Man has power on earth to forgive sins"). Assuming that the Gospels are accurate, Lewis said there are three options:

Jesus was telling falsehoods and knew it, and so he was a liar.
Jesus was telling falsehoods but believed he was telling the truth, and so he was insane.
Jesus was telling the truth, and so he was divine.
Thus, Lewis maintained that one cannot argue Jesus was merely a great moral teacher because his moral teachings would be invalidated by virtue of either his lying or his insanity. On the other hand, if he was divine, he must clearly be more than merely a great moral teacher.

Portrayals of Lewis' life
Recently there has been some interest in biographical material concerning Lewis. This has resulted in several biographies (including books written by close friends of Lewis, among them Roger Lancelyn Green and George Sayer), at least one play about his life, and a 1993 movie, titled Shadowlands, based on an original stage and television play. The movie fictionalizes his relationship with an American writer, Joy Gresham, whom he met and married in London, only to watch her die slowly from bone cancer. Lewis' book A Grief Observed describes his experience of bereavement, and describes it in such a raw and personal fashion that Lewis originally released it under the pseudonym "N. W. Clerk" to keep readers from associating the book with him (ultimately too many friends recommended the book to Lewis as a method for dealing with his own grief, and he made his authorship public).