I always thought of Tom Bombidil as Eru, the creator, or at the very least was taking cues from Eru. Two pieces of evidence: 1) The song he gives, which seemed a positive one, and is not remarked upon as discordant or unpleasant. Eru created through song, and in that choir it was the introduction of disharmony that signified evil. 2) The passage where it's asked "who is he?" The answer is "He is." And then "he is as…
I take a different view:
Eru knew who Melkor was from the start, and his “disharmony” was part of a broader and richer song — as shown by the duet that led to man and the ultimate downfall of evil lords.
The only time Eru spoke to Melkor, he chided him for thinking that a being of his own essence was acting outside his intent or marring the music.
If you take the Valar as aspects of Eru, then Melkor is the internal critic that drives genius to greater heights.