Final answer:
Grendel terrorized and ravaged Hrothgar and his people for twelve years.
Step-by-step explanation:
The question is asking for the number of years that Grendel terrorized and ravaged Hrothgar and his people. The story of Grendel and Hrothgar is from the epic poem 'Beowulf', which is an important piece of Old English literature.
In the poem, Grendel is described as a monster who terrorizes Hrothgar and his people in their mead hall, Heorot. Grendel attacks and kills the warriors in the hall every night for twelve years.
Therefore, the answer is that Grendel terrorized and ravaged Hrothgar and his people for twelve years.