Final answer:
The subject of the question is English, and the quoted line is an example of a metaphor from a poem.
Step-by-step explanation:
The subject of the question is English. The quoted line is an example of a metaphor, which is a figure of speech that compares two things without using the words 'like' or 'as'. In this metaphor, Grendel, the character from the poem, is described as a 'shepherd of evil' and a 'guardian of crime', emphasizing his menacing and destructive nature.