What was C.S. Lewis’s birth name before he became known by his initials?

C.S. Lewis’s birth name was Clive Staples Lewis.

Lewis was born Clive Staples Lewis on 29 November 1898 in Belfast. “C.S.” represents his first and middle names, Clive Staples, while Lewis is his family name. He was widely known as C.S. Lewis in public life and as “Jack” to friends and family.

The nickname “Jack” began in childhood after the death of a beloved dog named Jacksie. The young Lewis reportedly insisted that he should be called Jacksie, later shortened to Jack. That private name remained with him throughout his adult life, even while his books were published under his initials.

His middle name, Staples, came from his mother’s family. Readers sometimes expand the initials incorrectly or assume that “C.S.” was a pen name. It was not: the initials were a shortened form of his given names, and Lewis used them on his published books.