Grendel was the name of this grim demon
Haunting the marches, marauding round the heath
And the desolate fens; he had dwelt for a time
In misery among the banished monsters,
Cain’s clan, whom the creator had outlawed
And condemned as outcasts. For the killing of Abel
The Eternal Lord exacted a price:
Cain got no good from committing that murder
Because the Almighty made him anathema
And out of the curse of his exile there sprang
Ogres and elves and evil phantoms
And the giants too, who strove with God
Time and again until He gave them their reward.

Beowulf, Seamus Heaney (trans.)

Lines 102-114: The demon Grendel, who represents the ultimate evil in medieval Scandanavian culture, is the descendant of Cain, the man who killed his brother.