Grendel is one of the three monsters that are defeated by Beowulf in the story with the same name written in the 6th century.
Grendel is a temperamental monster who is capable of rational thought as well as irrational bursts of anger. Despite his extreme brutality and nasty habits, there is not much that separates him from human behavior. In the latter stages of his life, prior to his defeat to Beowulf, he embarks on a quest to understand human behavior.