The poet is an unnamed character, but scholars generally agree that it refers to Ellery Channing, one of Thoreau's closest buddies. But boo on the scholars. It's almost better for him to be anonymous. Like the philosopher and the hermit, the poet's lack of a name draws attention to the fact that he's a poet and forces us to think about the qualities that make him so great at what he does. For Thoreau, it isn't just verbal virtuosity that makes a good poet. You have to be morally sound as well. "Nothing can deter a poet," writes Thoreau, "for he is actuated by pure love" (Former Inhabitants.20).
The poet is a cheerful and optimistic presence in Thoreau's life, a great friend that he enjoys laughing and fishing with. In this respect, he's much like characters such as the philosopher and the woodchopper. In the mock dialogue with the hermit at the beginning of the "Brute Neighbors" chapter, the poet reminds the hermit that he must avoid getting caught up in philosophical reflection and instead immerse himself in the world, even if that just means goin' fishin' with a friend. This guy is what we call down-to-earth – not something we necessarily expect from a poet.