The Covenant is an interstellar religious cult empire, with the goal of ascending to the heavens using the ancient artifacts made by the extinct race known as the Forerunners. The Forerunners had left behind numerous artifacts of advanced technology, one of the artifacts being the Halo Array. Which the Covenant believe can allow them to live with the Forerunners in heaven.
Starting as an alliance between the Prophets (San'Shyuum) and the Elites (Sangheili) soon transformed into their high religion with the Prophets as religious leaders and the Elites as military leaders. Setting out into the galaxy, plundering and raiding other planets and aliens races all to find the artifacts. As they traversed the Milky Way they had species like the Grunts (Unggoy) or the Jackals (Kig-Yar) join their religious conquest as well as many other species.