What was C.S. Lewis’s childhood nickname?

C.S. Lewis’s childhood nickname was Jack.

Lewis was born Clive Staples Lewis, but he adopted the name Jack during childhood. The change followed the death of his childhood dog, Jacksie, who had been struck by a car. Lewis reportedly said that from then on he would be called Jacksie, which gradually became Jack.

The name remained important throughout his life. Family members and close friends generally called him Jack, while his published works used the initials C.S. Lewis. Readers sometimes assume that C.S. stood for his everyday first name, but the initials came from his given names, Clive Staples.

His brother Warren, known as Warnie, was another enduring presence in Lewis’s life. The brothers later lived together and Warren became an important source for biographical information about their household and travels.