C.S. Lewis's first name was Clive.
He was born Clive Staples Lewis in Belfast, Ireland, on 29 November 1898. “C.S.” represented his first and middle names, while “Lewis” was his surname. Friends and family often called him “Jack,” a nickname he adopted after a childhood dog named Jacksie died.
Lewis became known publicly by his initials rather than by the name Clive. The initials also helped distinguish his scholarly and literary work from the more private person known to friends as Jack. He later became one of the twentieth century’s best-known Christian writers and literary scholars.
A common mix-up is assuming that the “S” stood for a surname or that his familiar name was Clive. His full birth name was Clive Staples Lewis, and Staples was his middle name, taken from his mother’s family.