Grendel is described as descending from Cain in the Old English poem Beowulf. Cain, known in Genesis as the first murderer, becomes the biblical ancestor of the poem’s hostile and supernatural beings.
This ancestry connects Grendel to a Christian explanation of evil within a story that also contains older Germanic heroic and mythological elements. Grendel is portrayed as an outcast from God’s joy, and he attacks King Hrothgar’s mead hall, Heorot, after being tormented by the sounds of human celebration.
Grendel terrorizes Heorot for twelve years before Beowulf arrives. Beowulf fights him without weapons and tears off his arm, mortally wounding him. Grendel later dies in his underwater lair, while Beowulf’s next opponent is Grendel’s mother.
The answer is not Seth, Noah or Abel. Abel is Cain’s murdered brother, while Seth is another son of Adam and Eve; neither is identified as Grendel’s ancestor in Beowulf.