Poe, I am afraid, is wholly lacking in that element of manhood which, for want of a better name, we call character. It is something quite distinct from genius—though all great geniuses are endowed with it... I have made Poe my enemy by doing him a service. In the last Broadway Journal he has accused me of plagiarism, and misquoted [William] Wordsworth to sustain his charge... Poe wishes to kick down the ladder by which he rose. He is welcome.
The Broadway Journal, which Lowell alludes to, was a newspaper founded by Briggs with John Bisco. The two brought in Poe within its first year as a one-third owner of the publication. Poe was enlisted specifically because of his reputation and ability to draw attention. Briggs, however, soon left his project when he saw how caustic Poe had become in his reviews. Bisco left soon after, leaving the Broadway Journal in debt and solely in the control of Poe. He did the best he could, but the journal folded within another year.
Lowell became part of the New England literary elite despite early difficulties in his career, and was happy to remove his connection to Poe. Lowell had published Poe's famous story "The Tell-Tale Heart," for example. Only a few months before this letter, in fact, instead of criticizing Poe's lack of character, Lowell had offered this view of him:
Mr. Poe has that indescribable something which men have agreed to call genius. No man could ever tell us precisely what it is, and yet there is none who is not inevitably aware of its presence and its power... It is not for us to assign him his definite rank among contemporary authors, but we may be allowed to say that we know of none who has displayed more varied and striking abilities... Mr. Poe is at once the most discriminating, philosophical, and fearless critic upon imaginative works who has written in America. It may be that we should qualify our remark a little, and say that he might be, rather than that he always is, for he seems sometimes to mistake his phial of prussic-acid for his inkstand."
The above quote was published in Graham's Magazine, February 1845.