Established nearly five thousand years before their devastating war with the humans, the Covenant military body was forged on an agreement between two space-faring alien civilizations—the San’Shyuum (Prophets) and the Sangheili (Elites)—around the proper exploration and analysis of Forerunner technology. Believing that these efforts would ultimately locate Halo, an array of ringworlds which they believed held delivery into the afterlife; they began scouring the galaxy in search of these artifacts, violently integrating species on worlds they razed in the process.
As the Covenant collective of species grew, its threat grew as well, until it came in contact with humanity. During the course of this protracted war, the Covenant’s internal framework could not be maintained and fell apart. At its breaking, the Sangheili momentarily sided with mankind to defeat their former allies, but the end of the war did not usher in peace. With their core ideals fractured, the Sangheili fell into civil war. Rising from these conflicts was a fringe-sect of Sangheili who, along with other species, were completely dedicated to the unraveling of ancient Forerunner mysteries and continuing the previous efforts of the Covenant.