A forerunner is also a type of postage stamp. See also Forerunner (Dungeons & Dragons)

The Forerunners are a race of aliens referred to in the Halo Universe. Little is known about them, but certain things can be acertained from hints located in the game.

The Forerunners constructed the Halos to contain the Flood (a dangerous species of mutative infection spores). It is revealed in Halo 2 that the Halos are weapons of last resort, used to destroy all life within a certain radius capable of carrying the Flood.

The alien alliance known as The Covenant exalts the Forerunners, even considering them demigods, but it is not known if this is religious propaganda or not. The Covenant have explained in the book The Flood that they received much of their technology (if not all of it) from the "Forerunners". A species in their federation of alien species called the "Prophets", who are supposedly part of a leader caste, evolved on a planet formerly inhabited by the Forerunners.

Near the end of Halo 2, 343 Guilty Spark explains that the Forerunners destroyed themselves along with other sentient life three radii of the galactic center by activating the Halos from The Ark. The Ark is believed to be on Earth; it is unknown whether it encompasses the entire Earth or is simply an installation or object located on Earth. The Ark's nature will not be revealed until Halo 3, but theorized locations for the Ark include New Mombasa, East African Protectorate (from Halo 2), Jerusalem, and Boston, Massachusetts (from the Haunted Apiary).

Some fans point to similarities between the Forerunners and the Jjaro, an equally ancient, powerful, and absent alien race from the Marathon series of games.