C.S. Lewis’s first name was Clive, although he rarely used it publicly.
He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898. As a child, he disliked the name Clive and adopted the nickname “Jacks,” later commonly called Jack by friends and family. The initials C.S. became the form most readers recognized.
The middle name Staples came from his mother’s family. Lewis’s older brother, Warren Hamilton Lewis, was known as Warnie, and the brothers remained close throughout their lives. Their shared interest in mythology, literature, and invented worlds strongly influenced Lewis’s later writing.
Lewis is often called C.S. Lewis in biographies, library catalogs, and academic writing, while friends who knew him personally generally used Jack. The name should not be confused with his pen name or with a separate author: C.S. Lewis was the standard literary name under which he published fiction, apologetics, and scholarly work.