In the Halo video-game series, what is Master Chief’s real name?

Master Chief’s real name in the Halo video-game series is John-117.

John was abducted as a child for the SPARTAN-II program, a secret military project intended to create highly capable soldiers for the United Nations Space Command. The program subjected its candidates to demanding training and dangerous biological augmentations. John became the most prominent surviving Spartan-II and eventually received the rank of Master Chief Petty Officer.

The number “117” is his military identifier, not a surname. Because the games usually call him Master Chief, many players encounter his personal name mainly in novels, terminals, cutscenes, and expanded-universe material. Other famous Spartan-IIs, including Fred-104 and Linda-058, have their own numerical designations, so the identifiers should not be confused.

The character’s full designation is commonly written John-117, while “Master Chief” describes his rank and role. The title is therefore not his birth name, and John-117 is the single canonical answer.