Beowulf is an Anglo-Saxon epic which features the hero, Beowulf, as he comes to save Hrothgar and his people from the marauder known as Grendel. 

We only have a few clues about why Grendel is so outraged by Hrothgar and the typical Anglo-Saxon revelries which happen at his mead-hall, Heorot. None of them are enough to justify Grendel's twelve years of murderous marauding, however, and all of Hrothgar's people are thrilled that Beowulf has come to save them by killing Grendel.

Beowulf boasts that he will lie in wait for the monster and then fight him without weapons, just as Grendel does his killing; and that is what he does. Grendel arrives at Heorot, not knowing what is ahead for him.

Higelac’s hardy henchman and kinsman

Held him by the hand; hateful to other

Grendel is sorely wounded.

Was each one if living. A body-wound suffered

The direful demon, damage incurable

His body bursts.

Was seen on his shoulder, his sinews were shivered,

His body did burst. To Beowulf was given

Glory in battle; Grendel from thenceward

Must flee and hide him in the fen-cliffs and marshes,

Sick unto death, his dwelling must look for

Unwinsome and woful; he wist the more fully

The monster flees away to hide in the moors.

The end of his earthly existence was nearing,

His life-days’ limits.