Halo: Combat Evolved

Humanity is in the midst of a long war against an alien alliance called the Covenant which has been wiping out colony after colony. Your hero is Master Chief, who is given no name beyond his rank in the game itself. He is stationed on the Pillar of Autumn, a ship which, per protocol makes a jump in a random direction to retreat to avoid revealing the location of Earth. They find themselves at the titular Halo, a planet-sized ring of mysterious origin, and function with the Covenant on their heel...