C.S. Lewis’s surname was Lewis. His complete name was Clive Staples Lewis, and “Lewis” is the family name used in his author identity and scholarly career.
The question can seem deceptively simple because “Staples” is part of Lewis’s full name. Staples was his middle name, inherited from his mother’s family. Lewis’s initials therefore represent Clive Staples Lewis, not a shortened version of a longer surname.
Lewis published under “C.S. Lewis” across several genres, including literary criticism, Christian apologetics, science fiction, and children’s fantasy. His surname is also the name readers encounter in citations of works such as The Abolition of Man, Out of the Silent Planet, and The Chronicles of Narnia. He is sometimes confused with other writers named Lewis, but the initials and the Oxford context identify the Belfast-born author discussed here.