As someone who's read the books more times than I can count, I love finding Lord of the Rings fan theories that actually hold up under scrutiny. One of my favorites is that Tom Bombadil is actually the physical embodiment of Middle Earth itself, which explains why he's unaffected by the Ring's power. He's not a person, he's the land.
What other theories about Tolkien's world have you come across that actually make sense when you examine the evidence? I'm particularly interested in theories about Gandalf's true nature or what happens to the Elves after they sail West.
One of my favorite Lord of the Rings fan theories is that the Ents are actually what happen to Hobbits who live too long. Think about it - both are peaceful, connected to nature, love food and drink, and are resistant to corruption. The Ents have forgotten about the Entwives, and Hobbits have largely forgotten their own history.
There's even some textual evidence - Treebeard says Hobbits remind him of something he can't quite remember. It's one of those theories that make sense when you consider Tolkien's themes of decay and memory loss over long ages.
I love the theory that Gandalf is actually one of the Blue Wizards who returned to Middle Earth. The Blue Wizards went east and were never heard from again in the main narrative, but Tolkien later wrote that they might have played a role in weakening Sauron's forces in the east.
What if Gandalf is actually Alatar or Pallando, returning in a new form after failing in his original mission? It would explain why he seems to know more than he should about the wider world, and why he's so determined to redeem himself by helping defeat Sauron this time. It's one of those Lord of the Rings fan theories that adds depth to his character.
The theory about Tom Bombadil being the physical embodiment of Middle Earth is interesting, but I prefer the one that he's actually Eru Ilúvatar (God) in disguise. He's unaffected by the Ring because he created the world the Ring exists in. He's cheerful and sings because he's happy with his creation. He lives in the Old Forest because that's where the world is still closest to its original state.
The evidence is mostly circumstantial, but it fits Tolkien's Catholic worldview - God exists in his creation but doesn't directly intervene in free will. Tom helps the hobbits but doesn't solve their problems for them. It's one of those theories that make sense thematically even if there's no direct proof.
What about the theory that the Elves sailing West is actually them leaving the physical world for the spiritual realm, and that the Undying Lands are basically Heaven? It would explain why mortals can't go there except in special circumstances - you can't go to Heaven while you're still alive.
The symbolism in Tolkien's work is deeply Catholic, so this fits. The Elves are like angels who can choose to stay in the world or return to God. Men are like humans who have to live with mortality. It's one of those Lord of the Rings fan theories that connects the fantasy elements to real world religious concepts in a meaningful way.