C.S. Lewis’s first given name was Clive. He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898, and later became widely known by his initials rather than by his first name.
Lewis disliked the name Clive during childhood and adopted the nickname “Jacks.” The nickname came from a childhood incident involving a dog named Jacks, and friends and family continued using it for much of his life. “Jack” became the name by which many acquaintances knew him.
The initials C.S. stood for Clive Staples, while Lewis was his surname. The middle name Staples came from his mother’s family. Readers sometimes assume the C stood for Charles because initials can obscure a writer’s full name, but Lewis’s documented birth name was Clive Staples Lewis.
This naming detail also helps distinguish Lewis from other writers whose initials form a pen name. His best-known works include The Chronicles of Narnia, Mere Christianity, and The Screwtape Letters, all published under C.S. Lewis.