Grendel is the epitome of all evil in Beowulf. The narrator explains Grendel's ancestry at the beginning of Beowulf. The monster is a descendent of Adam and Eve's son, Cain, whose jealousy led him to kill his twin brother Abel:
"From him awoke all those dire breeds: ogres, elves, and phantoms that warred with God a lengthy while; He paid their wage to them!" (Chapter I).
The narrator characterizes Grendel as a low creature, driven by jealousy and bitterness, a hater of all things pure or of the light. The proud hall of Heorot tormented Grendel with its grandeur and music celebrating the Creation. Grendel, "a fiend of hell began to work evils," and part of his grim plan included taking control of Heorot in order to stop the glad and cheerful harp music of the golden hall (Chapter I). Grendel's attacks reveal him to be malevolent and vicious, murdering men in their sleep and on occasion, stealing their bodies back to his lair to be devoured.
One of the many defining points of Grendel's character is that not only does he commit such terrible, repeated acts of murder, but he also that he "think[s] nothing of this atrocity; such was the guilt in which he was steeped" (Chapter II). Grendel reveals himself as a remorseless killer, a creature beyond redemption or sorrow.