Like which elements were influenced by Christianity, and which elements by Celtic and other mythologies. I have heard that Gandalf was meant to be Odin. I'm wondering how much all this is so? Because I know Tolkein was a devout Roman Catholic.
As it happens, I wrote my undergrad thesis on Tolkien, and I had a section in which I discussed just this question!
He would have said that the work was influenced by language more than anything else. It was language that first led him to create the elements of Middle Earth, although the stories themselves also had root in a friendly agreement he had made with his close friend CS Lewis to both write stories. His poetry shows deep deep resonances of Anglo-Saxon influence, and his created languages are admirably drawn from various tongues of Northern Europe and the British Isles-- in the latter case, mostly Welsh, a tongue of which he was fond, though he claimed incomplete fluency in it.
Tolkien did not think that his stories were Christian works, though he admits frankly in his correspondence that part of the reason that the early parts of what were eventually incorporated into the
Silmarillion (specifically, the
Ainulìndalë and the
Valaquenta) were structured the way that they were in part because they needed to be satisfactory to a mind that believed in the Holy Trinity and the Blessed Mother (as he put it). Nonetheless, as he himself noted in the forward to the second edition of
Lord of the Rings, he disliked allegory in all forms, and strongly resisted the idea that his works were any sort of allegory, religious or political.
Some Christian influence, of course, cannot be doubted, and he himself did not deny it. There is no Illuvatar, no Melkor, without the Christian God the Father and Lucifer the Fallen One. A correspondent of Tolkien's (who may have been a priest, if I recall correctly) compared Galadriel to the Virgin Mary, and while Tolkien denied an equivalence in his imagination or intent, he at least tacitly admitted to some influence in terms of the emotional freight with which he sought to lade his descriptions of her.
Interestingly, though, Tolkien was quick to point out the relative absence of practical religion in his created world; the Elves had none, he said, and in his own words, the spiritual practices of the Dúnedain of Númenor were an austere absolute monotheism more akin to Maimonidean Judaism than to Christian observance.
As for mythology, Tolkien claimed to be much influenced by the old
Kalevala, which is the collection of Finnish poetic cycles written down in the 19th Century as a national epic. There can be no doubt that he was very much influenced by the Norse
Eddas, and the
Niebelungslied. Some of the names he uses in
The Hobbit and
Lord of the Rings come right out of the
Elder Edda.
Beowulf, and perhaps also the Middle English
Sir Gawain and the Green Knight (which Tolkien also translated, in an extremely successful poetic rendering) were influences as well. He was almost certainly influenced by the
Mabinogion (the collection of poetic cycles which are the Welsh national epic), and perhaps also
Trioedd Ynys Prydain (
The Welsh Triads, a Welsh/Arthurian collection of wisdom epigrams and hints of tales).
Tolkien himself rejected claims of any resemblance of his works to Irish mythology: he apparently disliked Irish mythology, finding little love for what he saw as its vigorous drinking and sex, and its gleefully embroidered violence. But he did admit, at least tacitly, to some small influence by the various Arthurian cycles.
I don't know that there can really be any measuring of how much influence of Christianity versus how much influence of mythology there can be. Ultimately, all influences were completely filtered through Tolkien, and he was greatly successful at blending his influences seamlessly into a unique and novel product.
