C.S. Lewis’s middle name was Staples. The author’s full birth name was Clive Staples Lewis, so the initials C.S. Lewis stand for Clive Staples Lewis.
The name Staples came from his mother’s family. Lewis generally published under his initials rather than using his full given name, and the abbreviated form became one of the best-known author names of the twentieth century.
Readers sometimes assume that the S stands for Samuel because that is a common English given name, but it was Staples. The name is also sometimes confused with Lewis’s nickname, “Jack.” That nickname came from a childhood incident involving a dog named Jacksie and became the name by which friends and family commonly knew him.
Lewis used several different literary forms during his career, including Christian apologetics, literary criticism, fantasy, science fiction, autobiography, and sermons. Across those fields, “C.S. Lewis” remained the consistent professional identity attached to his books and essays.