The races of the Halo universe
There have been dozens of sapient species that have called the Halo universe home. For millions of years the galaxy was dominated by the Forerunners, who enacted their will upon any other species that threatened their dominance. Only the Flood, who originated from an even more ancient species known as the Precursors, were able to put an end to the Forerunner civilization, forcing the Forerunners to activate the Halo Array and commit galactic genocide against all sapient species.
One-hundred thousand years later the galaxy, having been reseeded by the Librarian and the Forerunner Conservation Measure, saw the rise of humanity to prominence. This rise was seemingly unstoppable until 2525 when they made first contact with the Covenant hegemony, introducing the entire human race to over half a dozen distinct sapient alien races, all with a desire to wipe humanity off the map.
SangheiliAn honorable warrior species who was one of the founding members of the Covenant.
UnggoyA relatively small, methane-breathing species who tend to get exploited by more powerful races.
FloodA deadly disease created by the Precursors that converts all sapient species into a new vector for infection.
ForerunnersAn ancient race who battled the Flood and built the Halo Array to defend against them.