Gears of War is a tactical third-person shooter video game developed by Epic Games using Unreal Engine 3.0 technology and published by Microsoft Game Studios. Gears of War centers around the soldiers of Delta Squad as they fight to save the human inhabitants of the fictional planet Sera from a relentless subterranean enemy known as The Locust Horde. The player assumes the role of Marcus Fenix, a former prisoner and war-hardened soldier. In cooperative play, the second player plays as Fenix’s friend and fellow soldier, Dominic Santiago. The two soldiers join up with Delta Squad and battle the Locust Horde through the course of an action-packed campaign.

The game achieved major success after its release. On November 20, 2006, Gears of War became the most popular game on the Xbox Live service, overtaking Halo 2, which had held the spot since its launch in November 2004. It was named the GameSpot Game of the Year. By January 19, 2007, just ten weeks after its debut, over three million units of the game have been sold.