According to the commentary in the Art of Metal Gear Solid 4, a large part of the reason why it was designated as being separate from the titular mechs was as a compromise, as they were originally intended to be an actual set of Metal Gear, but due to the radical evolution of the concept with REX, RAY, and to a lesser extent the Shagohod, it was not interesting to merely have it launch a missile. Following a short Policenauts stint, Kojima asked Shinkawa to work on a new game that was in the pre-production phase. In an act of sacrifice, he got off a few more shots from his gun, succeeding in destroying the radome completely, and forcing Liquid to open the cockpit to see, though Fox was killed beneath REX's trampling feet shortly afterward. In 2020, movie director Jordan Vogt-Roberts teased a Metal Gear Solid cinema adaptation, releasing concept art for his film. With REX now marginally operational, Snake and Raiden climbed aboard, with the former taking the controls to pilot it out of the hangar.

Like with Metal Gear Online before it, REX's likeness is utilized as a head accessory for various soldiers in Metal Gear Survive. It is less armored than the rest of the head and is therefore vulnerable to gunfire, though it requires a very long, sustained burst to penetrate the armor. Metal Gear REX appears alongside Metal Gear RAY and Metal Gear Gekko on the Shadow Moses Island stage in Super Smash Bros. Attached to the hips were a pair of very strong legs with three-toed clawed feet and a single large claw on each heel.In The Twin Snakes, REX shares the same boss BGM theme as the Hind D, similar to Metal Gear 2: Solid Snake with the Hind D and Metal Gear D. We also do not accept products that are intimate or sanitary goods, hazardous materials, or flammable liquids or gases.

Metal Gear REX is named after the Tyrannosaurus rex, due to its theropod-like design; other similarities include the open cockpit's resemblance to a gaping mouth, along with its ability to roar.This explains the "energetic brushstrokes" Kojima talks about: the human figure has no mysteries for him, as the artist is liberated from having to think about anatomic details, or even the management of his strokes. The two were eventually rendered inoperable after sustaining heavy damage, and Liquid made his retreat on foot towards his waiting ship. It is included in the Collector's Edition and Premium Package of The Phantom Pain for MGO-specific DLC via a code. As Liquid proceeded to step on Snake with REX once more, the machine suddenly began to lose its balance, the control systems having become inoperable from the cockpit damage sustained, and the resulting explosion knocking Snake unconscious. If he destroyed one with a very high-caliber weapon, the other was immediately awakened by the explosion.