Who designed the Metal Gear REX weapon in the original Metal Gear Solid?

Hal Emmerich designed Metal Gear REX in the original Metal Gear Solid.

Emmerich is a scientist working at the Shadow Moses nuclear disposal facility. He is coerced into helping develop REX, a nuclear-capable bipedal weapons platform designed to launch nuclear missiles while using its rail gun to bypass conventional missile defenses. Solid Snake encounters Emmerich after discovering the consequences of the project.

Emmerich is better known by his nickname, Otacon, which comes from his interest in anime conventions. He becomes one of Solid Snake’s closest allies and later helps establish and operate Philanthropy, an organization opposed to Metal Gear proliferation. A common mix-up is treating Otacon as a different character from Hal Emmerich; they are the same person. The surname also connects him to later scientists in the Emmerich family.