Halo: Combat Evolved

Humanity is the midst of a long war against an alien alliance called the Covenant who have been wiping out colony after colony. You 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 make 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 heels. Master Chief must repel the Covenant assault and discover the secrets of Halo with the assistance of the female AI Cortana who lives in his suit and gives missions.