C.S. Lewis’s full first name was Clive. He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898.
The initials “C.S.” came from his first and middle names, Clive Staples. Lewis rarely used “Clive” in everyday life. As a child, he adopted the nickname “Jack,” reportedly after a childhood dog named Jacksie died. Friends and family continued calling him Jack for much of his life.
Lewis’s middle name, Staples, came from his mother’s family. His father, Albert James Lewis, was a solicitor, while his mother, Florence Augusta Hamilton Lewis, had studied mathematics and logic. Lewis’s early education took place in Ireland and England before he became a scholar of literature and medieval history.
The name “C.S. Lewis” became internationally associated with works including The Chronicles of Narnia, Mere Christianity, and The Screwtape Letters. “Clive” is therefore his first name, not an abbreviation of the initials used in his pen name.