From Quake Wiki

According to the storyline for Scourge of Armagon, this creature is the general of Quake's forces, planning to invade Earth via a portal known as the 'Rift'. Physically, Armagon resembles a giant Gremlin with cybernetic legs and a combined Rocket Launcher/Laser Cannon for arms. This gives the creature an appearance not unlike the Cyberdemon from Doom and the Strogg in Quake II.