Hehe, I'm not at all convinced he did. The way I understand it, Bombadil was originally one of his kid's toys, about which he began to make up poems and stories. Eventually, Bombadil found his way into LoTR: a decision which, as a writer myself, I have to view as far more sentimental than practical.

In fact, that's why I was a Bombadil hater for a very long time. I didn't see that he had any plot point or artistic merit. It was only when I attempted to consider his place within the larger mythos, which necessarily involved my own theories, that I started to see a certain merit in him.

Which is really the way a lot of Tolkien's work has gained so much appeal and significance to me, not taken by itself but as part of some grand whole. ^_^