[Gurthang]

There is but one conclusion that can be drawn. Only one. Evidence clearly shows that Tom is none other than Sauron himself! I shall explain.

Clearly, if Tom was Merry or a famous runner, both mortal, he would have disappeared under the Ring's dreadful power. Yet the fact that he did not vanish points out that he was not mortal, cancelling out any possibilities of Merry or a futuristic fasty.Also, upon wearing the Ring, Bombadil exhibited no desire whatsoever to keep it from Frodo, a feat Gandalf did not even attempt! The Ring had no power over Tom, because Tom was truly its maker.

Now, you're thinking, 'if it was Sauron, he would have taken the Ring right then'. But no, he would not. He was in a weak state(due to lack-of-Ring-itus), and would need time to recover from his illness. Even taking back the Ring, he would have been enormously defenseless during his long trek home. He foresaw that they would bring the Ring closer to him, and he let them do so.

Now he was there mostly for recon work, and for his longing to hold his Precious, if for only a time. Once he was certain that the Ring would be taken somewhere(as opposed to thrown into the sea) he was satisfied to watch. At this time he also pointed his Nazgul directly to the Ring. This is why they caught up to the Hobbits at Bree, very soon after their separation from Tom.

This case is solved, Bombadil was Sauron.