C.S. Lewis’s first and middle names were Clive Staples.
He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898. “C.S.” therefore represents his first two given names rather than a shortened form of a longer literary pseudonym. Friends and family often called him Jack, a nickname he adopted during childhood.
Lewis’s brother Warren was known as Warnie, and the two remained close throughout their lives. Lewis became famous as a literary scholar, Christian apologist, and author of fiction, but his formal name appears on his academic and publishing records.
A common mix-up is assuming that “Jack” was Lewis’s middle name. It was instead his preferred nickname. His initials are also sometimes written without periods as “CS Lewis,” especially in modern publishing and online references.