[The Might]

I am definitely not a Bombadil expert, since he never interested me that much, I was content leaving him as what he is meant to be - an enigma.
But as far as I know The Adventures of Tom Bombadil were published in 1962, but he already existed as a character before.
What I have however learned in a very interesting thread a long time ago, he is in M-e, but not of M-e, more like an outsider, an intruder in the world.
The explanation for his existence is of course hard to find, most likely a product of the music in the beginning, but he was actually more like "thrown" into the world by Tolkien.