The author (or authors) of this poem are anonymous. We don’t know who came up with it. But we can recognize it as a Navajo song because it has a lot of features in common with other Navajo songs that form part of the Mountain Chant ceremony.
The songs that make up the Mountain Chant ceremony often use repetition. In “Twelfth Song of Thunder,” there’s a lot of repetition of words and phrases. We can find similar patterns of repetition and refrain in other songs such as “Sixth Song of the Mountain Sheep” and “Sixth Song of the Holy Young Men.”