C.S. Lewis used the nickname Jack throughout most of his life.
Lewis’s birth name was Clive Staples Lewis, but he became “Jack” as a child. After the death of his beloved dog Jacksie, young Lewis reportedly began using Jack as a personal name. The nickname stayed with him through school, military service, Oxford, and Cambridge.
Friends and colleagues commonly called him Jack, while his published books appeared under C.S. Lewis. This difference can confuse readers who encounter references to “Jack” in biographies, letters, or accounts of the Inklings. “Jack” does not refer to a separate author or fictional character.
Lewis’s close friend J.R.R. Tolkien also knew him as Jack. The two writers met at Oxford and shared interests in mythology, language, literature, and Christianity. Lewis’s private nickname therefore appears frequently in correspondence and memoirs, even though the public literary name remained C.S. Lewis.