The forerunners

Long before humanity shed its own terrestrial bonds, an ancient race known as the Forerunners had already mastered the heavens. Using their advanced technology they took it upon themselves to protect all life in the galaxy. But when a threat emerged from the blackness beyond our stars, the Forerunners were caught off guard.

The Flood, a parasitic species that propagates by infecting sentient beings, had already infested a variety of worlds within the Milky Way. By the time the Forerunners took action, it was too late; the Flood had already surpassed any efforts at containment.

another great post dude, love owning the flood with a shotgun