Dungeon Master describes the beholder as "a foul and evil beast that came up from the Underworld and destroyed all things of beauty." It is a creature that fires assorted energy beams and tentacles from its eleven eyes and guards a portal home. It's lair is dubbed the Valley of the Beholder; a once beautiful valley that it has rendered barren. Sir John defeats the beholder with a flower that Diana gave him, it promptly deflates and sinks into a fissure, revealing an ocular style portal home.
In the 1987 Dungeons & Dragons annual the comic strip version of The Eye Of The Beholder is called The Eye Of The Watchman, similarly with the beholder being referred to as a watchman instead.