[The Squatter of Amon Rûdh]

In the early drafts of LotR, Tom calls himself 'Aborigine', not 'Eldest'. As Christopher Tolkien observes in his footnotes, the likely times for Tom to come into being are before the flight of Melkor and Ungoliant or, more likely, during the time in which Melkor was banished in the Void. Since Tom remembers the dark beneath the stars when it was fearless, Varda's star-kindling must have taken place before his memory begins, and therefore he was not alive when the Dark Lord originally entered Arda, first of all the Valar. That basically blows all of the 'Tom is an aspect of Eru', 'Tom is the spirit of Middle-earth' and 'Tom is a forgotten Maia' theories I've seen out of the water and leaves us with a character who is an anomaly. He's not exactly an Elf, certainly not a Dwarf, and while he could be a Man (the most likely explanation in my opinion), his great longevity is difficult to explain. In his letters, Tolkien points out that Middle-earth is an imperfectly conceived universe, and all but tells his correspondant that Bombadil can't be made to fit at all.

Personally Bombadil strikes me as Adamic, which might explain his long life. We might, I suppose, take him to be an image of unfallen Man, blessed with length of years and a disdain for worldly concerns, but even that would take some explaining, since he was in the lands about the Shire before the Elves first passed through. Tolkien was probably right: philosophizing does not improve him. My instinct is to accept the character as a mystery and mark up all inconsistencies with the main mythology to the vagueries of the branching acquisitive theme. After all, Tom was conceived long before he was made a part of Middle-earth, and it's perhaps inevitable that some of the joins should still show.