Number Four, or as he names himself, “John Smith,” is an alien from the planet of Lorien and the protagonist of the novel. He is a member of the Garde, a subspecies of Lorics gifted with supernatural abilities known as Legacies. It is the Garde’s duty to defend the planet of Lorien from their enemies and invaders, the Mogadorians. Garde members serve to protect, while the Cêpans, who act as the Garde’s keepers, serve to govern the planet and support the Garde as they develop their Legacies, or supernatural powers. Henri is Four’s Cêpan, and he acts as a father figure and mentor to Four throughout the novel.

The Garde are made up of nine members, and as the title of the novel indicates, “John” is Number Four. The Mogadorians can only kill the Garde members in order of their numbers, and One, Two, and Three have already been killed, leaving Four next in line. The danger that Four will be discovered is the driving problem throughout the novel, as Four and Henri move from town to town on Earth in hopes of remaining hidden. Their inability to remain in one place for too long is the main reason for Four’s feelings of loneliness: Four is a 15-year-old boy who has never lived a normal life and has no identity to call his own on Earth.