Halo 2 is a first-person shooter developed by Bungie and the sequel to Halo: Combat Evolved. The campaign alternates between two playable characters: the human supersoldier Master Chief and the Covenant warrior known as the Arbiter. The game introduced online multiplayer via Xbox Live with an automated matchmaking system, dual-wielding of certain weapons, and vehicle hijacking. It supports both cooperative campaign and competitive multiplayer modes, and was the best-selling game on the original Xbox.

In the 26th century, the Covenant, a powerful alliance of alien races, launches a surprise attack on Earth. Master Chief defends the planet's orbital stations before pursuing the Covenant fleet to a second Halo installation. Meanwhile, a disgraced Covenant Elite commander is branded a heretic for failing to prevent the first Halo's destruction and given the suicidal rank of Arbiter. As both warriors pursue their separate missions, they uncover a brewing civil war within the Covenant and a parasitic threat that endangers all sides.