Metal Gear REX is a Metal Gear model that made it's appearance in Metal Gear Solid for the PlayStation and it's remake, Metal Gear Solid: The Twin Snakes for the GameCube. Metal Gear REX was designed by Hal "Otacon" Emmerich and uses a rail gun. The weapon is used by Liquid Snake, Solid Snake's genetic brother.
In Super Smash Bros. Brawl
Metal Gear REX is a hazard in the background of the Shadow Moses Island stage in Brawl. What it does is unknown.