Final answer:
Grendel is best described as being angry towards mankind, as shown by his actions in the epic poem 'Beowulf'.
Step-by-step explanation:
The characteristic that best describes Grendel is angry towards mankind. Grendel is a character from the Old English epic poem 'Beowulf,' and he is depicted as a monstrous creature that holds deep resentment and anger towards humans.
His violent raids against the hall of Heorot are driven by this anger and his inability to participate in the joys and the society of men, which leads to his vengeful assault against the warriors of Heorot.