To put it in simple terms. Tolken came up with -everything- in those books. He even made up a couple of languages for it. Seriously, complete languages, with their own phonetics and lettering system. [He was a linguist.] He wrote all the songs, [there's several], and pretty much came up with the entire 'High Fantasy' genera with those books.
He even invented most of the creatures and races in the books. The idea of elves, dwarves, dragons and such were around. He's the one who pretty much set the standard for how they're used and represented in fantasy games, books, films, hell -anything- like that today. D&D and everything that came of it would not exist if not for these books. He's the original DM.
There is a lot of influence from Celtic, Norse, and other European mythology, The War [breeding an army], and religions. He was Catholic, but the books were influenced by other more pagan faiths as well.
It was written during the second world war, and published in the 1950's.
It's a direct sequel to 'The Hobbit' and has a partially written sequel called 'The Silmarillion' that was never finished.
Tolken did for Fantasy what Stoker did for Vampires with 'Dracula' and Romero did for Zombies with the 'Living Dead' films. All those standards and rules have their origins in these books, and he made it up himself.
He was one of those scary genius types. Even if you didn't like his books, if you're interested in anything that's 'sword and sorcery fantasy' at all, it probably never would have existed without these books. It's the first ancestor of pretty much all of it.