We know something about the 'author' of the
Narn i Hîn Húrin, and about the background to his composition of the work, according to this note by Christopher Tolkien:
In an introductory note, existing in different forms, it is said that though made in Elvish speech and using much Elvish lore, especially of Doriath, the Narn i Hîn Húrin was the work of a Mannish poet, Dírhavel, who lived at the Havens of Sirion in the days of Eärendil, and there gathered all the tidings that he could of the House of Hador, whether among Men or Elves, or of Doriath. In one version of this note Dírhavel is said to have come himself of the House of Hador. This lay, longest of all the lays of Belariand, was all that he ever made, but it was prized by the Eldar, for Dírhavel used the Grey-elven tongue, in which he had great skill, He used that mode of Elvish verse which was called Minlamed thent / estent, and was of old proper to the narn (a tale that is told in verse, but to be spoken and not sung). Dírhavel perished in the raid of the Sons of Fëanor upon the Havens of Sirion. (
Unfinished Tales, (London: Unwin Paperbacks, 1982), p. 146, fn. 1.)
When I first read this note, I was impressed by the fact that this Man was so good at composing in an Elvish tongue that even the Elves liked his work.
It was, I later realised, somewhat fitting for a story that dealt with so much interaction between Men and Elves.