C.S. Lewis’s first name was Clive, although he became widely known by his initials rather than by that name.
He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898. “Staples” was his mother’s family name, and “Lewis” was his surname. As a child, he disliked the name Clive and reportedly asked to be called “Jack,” a nickname that remained with him among friends and family.
Lewis used “C.S. Lewis” on most of his books, including The Chronicles of Narnia, Mere Christianity, and The Screwtape Letters. The initials gave his authorial identity a formal, distinctive style, but they did not represent a longer first name. Readers sometimes assume the C stands for Charles or Christopher; it stands for Clive. His brother Warren was also known by a nickname, “Warnie,” in the Lewis family circle.