Immortalized for geeks via copious usage as a NetHack creature mis-identifier. Creatures would be mis-identified when your character was in "Hallucination" status (most commonly incurred by quaffing a potion of hallucination, or encountering an exploding black light), and unable to tell what a creature really was. The usual message upon seeing a creature (friendly or not) would identify the creature and its action like so:

"The water nymph tries to seduce you!"

This would be replaced by:

"The one-eyed, one-horned flyin' purple people eater tries to seduce you!"

The creature mis-identification would change every instance of an action being observed (i.e., almost every turn), but the one-eyed, one-horned flyin' purple people eater was not only the longest mis-identifier, it was also one of the few fictional ones (most mis-identifiers would display random names of actual in-game creatures). That combination made it easy for the one-eyed, one-horned flyin' purple people eater to lodge in the mind of the player.