C.S. Lewis commonly used the name Jack instead of his first name, Clive.
Lewis’s full name was Clive Staples Lewis, but he was known to family and friends as Jack. The nickname originated after the death of a childhood dog named Jacksie, an event that led Lewis to adopt “Jacks,” later shortened to Jack.
The name remained part of his personal identity throughout adulthood. Friends, colleagues, and members of his family generally called him Jack, while “C.S. Lewis” became the name under which his books were published.
This distinction can cause confusion because biographies often alternate between “Lewis” and “Jack.” “Clive Staples Lewis” is the formal name, but Jack is the established personal name associated with the author, Oxford don, and Christian thinker.