C.S. Lewis’s first given name was Clive. He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898. His middle name, Staples, came from his mother’s family name.
Lewis disliked the name Clive from childhood and preferred the nickname “Jack.” The nickname reportedly arose after the death of his childhood dog, Jacksie, whom he had loved deeply. Lewis began calling himself Jack and asked family and friends to use that name.
“C.S. Lewis” is therefore a literary form of his initials, not the name he normally used among close friends. The initials stand for Clive Staples. He later became widely known as Jack Lewis in personal and academic circles, while his books appeared under C.S. Lewis.