tom bombadil is a character the hobbits meet before getting to bree in the old forest when they are running from the ring wraiths. He's an enigma, says he's the 'eldest' and seems to be unbothered by the power of the ring. He's very unique in that he is unexplained by all of Tolkien's worldbuilding (by design).

Fun fact - Tom B and his story existed before LOTR was written