Halo: Combat Evolved (Steam)

Bent on Humankind's extermination, a powerful fellowship of alien races known as the Covenant is wiping out Earth's fledgling interstellar empire. Climb into the boots of Master Chief, a biologically altered super-soldier, as you and the other surviving defenders of a devastated colony-world make a desperate attempt to lure the alien fleet away from earth. Shot down and marooned on the ancient ring-world Halo, you begin a guerilla-war against the Covenant. Fight for humanity against an alien onslaught as you race to uncover the mysteries of Halo.