The Guardians is a placeholder name shown when a player's character in a Halo game dies of unknown causes. When a player dies under bizarre or unknown circumstances, the message "<player> was killed by The Guardians" is shown. The message appears in Halo Combat Evolved, Halo PC, Halo Custom Edition, Halo 2, Halo 2 Vista, Halo 3, Halo 3: ODST, Halo: Reach, Halo 4, and Halo 5: Guardians.

The Guardians played a valiant defense during the Early hours of the Moderation War during the Viral Invasion, and were still remain active even after the permeant removal and fragmentation of the Xbox Live Administrators and Moderators from the Network. During the course of the Moderation War, the Guardians were redeveloped by Bungie into destroy Chaos forces as they roamed through the Map, these effects would also allow the Seven Sages to remain well defended in their main headquarters at Sandbox, which was surrounded by giant watchtowers, with barriers that kills any players attempting to go beyond.

The Guardians were shut down completely by Condemnation after the Fall of Sandbox about 13 hours after the Viral Invasion.