Answer:
Alliteration.
Step-by-step explanation:
In "Grendel" by John Gardner, the poetic device that the author used in the phrase "deeds of dead kings" is alliteration. Grendel is talking about what the Shaper said about the actions of glorious kings. He uses alliteration. This is a literary device in which the words begin with the same letter. In an alliteration, words can also belong to the same consonant or vowel sound.