Ur-grue
In the fourth Zork game, Beyond Zork, an evil being called an "Ur-grue" is introduced as the primary villain. Though similar in name, the Ur-grue is significantly different from the classic grue, being more akin to an evil god of darkness than a simple predatory monster.
Again, Scandinavian and German language may account for this etymology, where the Ur- prefix is used to signify origins. An Ur-grue would be the mother/father of all grues, or possibly the first grue.
Read more about this topic: Grue (monster)