Who or What is Tom Bombadil?

[narfforc]

Originally Posted by yavanna II

I've long ago decided for myself that Tom Bombadil is the very spirit of Arda--Arda in a physical form that can walk, talk, and be like a Kid of Eru in the sense that he's almost looking like them.

"Eldest, that's what I am ... Tom remembers the first raindrop and the first acorn ... He knew the dark under the stars when it was fearless — before the Dark Lord came from Outside."

Yes I agree in a way, the more I think of the history of Bombadil, the more I am convinced that he is either the Guardian of the Secret Fire/Flame Imperishable or he is the physical embodiment it. Why else would he come First, when there was nothing else in Arda apart from the Flame that Eru had placed there.