Metal Gear REX is a prototype Metal Gear model who made its first appearance in Metal Gear Solid for the PlayStation and its remake, Metal Gear Solid: The Twin Snakes for the GameCube. Metal Gear REX was designed by Hal "Otacon" Emmerich who had been lead to believe by his superiors that he was designing a defensive weapon. However, the real brains behind REX was Aleksandr Leonovitch Granin, who made the plans during the Cold War. In the PS2 game, Metal Gear Solid 3: Snake Eater, Granin revealed that he was going to send the plans to REX to his friend in America, ironically Otacon's grandfather, after the plan for the Shagohod, a tank-like nuclear weapon which could launch a nuclear strike from country to country, was chose over his plan. He was killed by Colonel Volgin before he could, as he was suspected of being a spy for the Unites States. Revolver Ocelot found these plans shortly after the events of the game. Amongst most of its typical weaponry - two Vulcan gatling guns, a missle launcher, and a laser - REX has a giant rail gun which uses magnetic power to launch nuclear warheads a great distance without the need for propulsion. This fearsome machine was piloted by Liquid Snake, Solid Snake's genetic brother. After REX was destroyed in MGS1, Revolver Ocelot sold the Metal Gear REX blueprints on the black market, allowing buyers all over the world to create their own Metal Gear REX. This necessitated the development of Metal Gear RAY, an anti-Metal Gear that would combat the various REX models. The repaired, original REX (with the exception of the rail gun which was removed for Liquid's purposes) also appears in Metal Gear Solid 4: Guns of the Patriots, with Solid Snake piloting it into battle against the original RAY, piloted by Liquid Ocelot (Liquid Snake in Ocelot's body).
In Super Smash Bros. Brawl
Metal Gear REX appears in the background of the Shadow Moses Island stage in Super Smash Bros. Brawl, bursting through the wall of the tank hangar and leering menacingly at the combatants on stage, but despite its immense size, it is not a threat as a hazard and will not attack other opponents on sight (despite looking like as if it is about to fire its railgun).
Trophy Description
A war machine of ruinous power. Metal Gear REX was developed at the weapons company ArmsTech under the eye of Hal "Otacon" Emmerich. It had the ability to launch nuclear warheads from a mounted rail gun. During testing, REX was captured by FOXHOUND, a rogue special-forces unit headed by Liquid Snake, but Solid Snake managed to destroy the machine before calamity ensued. This guy is a background character.