C.S. Lewis’s middle name was Staples.
His full name was Clive Staples Lewis, although he was usually known publicly by his initials, C.S. Lewis. The initials became especially familiar through his works of Christian apologetics, literary criticism, fiction, and children’s literature.
Lewis was called “Jack” by family and friends rather than “Clive.” He adopted that nickname during childhood and used it for the rest of his life. The name reportedly followed an incident involving a childhood dog named Jacksie, after which Lewis chose “Jacks,” later shortened to “Jack.”
Readers sometimes assume that the initials stand for a longer first name or for two given names. They do not: “C.S.” represents Clive Staples. The name “Lewis” came from his family, and “Staples” was inherited from his maternal family connections.