Inspired by Soviet-era designs for a bipedal tank, Metal Gear REX is a prototype mobile nuclear weapons system designed by Hal Emmerich. Emmerich was opposed to nuclear warfare, and was unaware of the mech’s purpose, believing REX to be a defensive armament. REX was left to rot after the Shadow Moses Island Incident, but it saw combat once again nine years later in a battle against Metal Gear RAY.