From Creatures Wiki
Grendels (Cyberlifogenis vicious) were a failed (and at the same time rather successful) genetic experiment by the Shee. Some consider them aggressive and vicious creatures, the arch-enemies of the Norns. Others, however, have more benevolent opinions of them. For more on this side of the story, check out the website The Truth About Grendels.
 Grendels in the Games
In Creatures the Grendel is found in a large tree (Yggsdrasil) near one of the oceans; in Creatures 2 it can usually be found near the Volcano, and in Creatures 3 they are generally found in the Jungle Terrarium.
Originally, Albian Grendels were a species reliant on a Queen (the Grendel Mother) for reproduction, however since then the species has become more reproductively active. Known subspecies include the dangerous, hunting, Banshee Grendels created by a subspecies of the Shee themselves, the Banshee, who mixed their own Shee genetics with Grendel ones.
 Background Information
In the Norse epic poem Beowulf, Grendel is a hideous monster with huge talons and gaping jaws, who frequently makes meals of men living in the land of Herot. He is a descendant of Cain, the first murderer. Beowulf, a prince of the Geats who had been summoned to help the men of Herot, defeats him bare-handed, ripping off one of his arms (which turns out to be a mortal wound). Grendel's mother, who is more powerful than Grendel himself, tries to avenge her son, but is defeated also by Beowulf, who lops off her head with a large broadsword after reaching her dark, underwater lair. Incidentally, Cain was the name given to the first naturally-born norn (see history).
A possible inspiration for the Grendel's appearance are the Bottersnikes from the book Bottersnikes and Gumbles here.
Browse the list of Grendel breeds!