Lewis is regarded ... as one of the most influential Christian apologists of his time. Mere Christianity was voted best book of the 20th century by Christianity Today in 2000. Due to his religious skepticism at first and his conversion at last, he is called "The Apostle to the Skeptics."
In 1948 he lost a debate with Elizabeth Anscombe at Oxford's Socratic Club over his argument in Miracles that naturalism was self-refuting. This loss led to his role as an apologist readjusted, and his future concentrated on devotional writing and children's literature. The weakness exposed in the debate made him substantially rewrite the related chapter for the next editions.
The Inklings informal literary discussion group around him at Oxford lasted some two decades between the early 1930s and late 1949.