Final answer:
Calling Grendel a "shepherd of evil" is an example of metaphor.
Step-by-step explanation:
The figurative language used in calling Grendel a "shepherd of evil" is an example of metaphor. Metaphor is a type of figurative language that describes one object using another for rhetorical effect, without using the words "like" or "as". In this case, Grendel is being compared to a shepherd, emphasizing their role in guiding and controlling evil.