But no mere mere Christian, he (C.S.Lewis) became arguably the leading popular Christian apologist of the 20th century, a defender and explainer of the faith who was hailed by popes, Protestant evangelists, politicians, and other world leaders for his brilliant yet accessible campaign against the rising tide of unbelief in the modern world.

http://www.usnews.com/usnews/news/articles/051212/12lewis.htm