Metal Gear Rex is a fictional bipedal nuclear-equipped walking battle tank featured in the video game series Metal Gear Solid. Designed by Dr. Hal Emmerich, REX represents a significant threat due to its stealth capabilities and ability to launch nuclear warheads from anywhere in the world. In the series, it serves as one of the main antagonistic forces, driven by its misuse by terrorist groups. Its appearance marks a turning point in the story, challenging the protagonist, Solid Snake.