"The Hobbit" and "The Lord of the Rings," both by J.R.R. Tolkien, are set in a place called Middle Earth. Any work of fiction needs to have a setting, and while Middle Earth is such a setting Tolkien goes far beyond what nearly any other author has done in terms of history and back-story. As an author myself I am amazed at what Tolkien accomplished.
Tolkien wanted to fill a gap that he perceived in the mythology of Great Britain. Whether he started out with that specifically in mind or whether that evolved as he wrote bits of stories that were set in Middle Earth, I'm not sure. But either way, the fruit of his life's work is truly incredible. Not only did he create a world in which his characters could live, and several races of characters, but he also created a number of functional languages including the alphabets for each. He wrote the histories for each race all the way back to the "creation" of Middle Earth's universe. He really went all out. But for all of his work and creativity much of the history and back-story of Middle Earth is never mentioned in either of Tolkien's most famous works, although they are available in "The Silmarillion" and other collections of Tolkien's writings. That history did shape his work and give "The Hobbit" and "The Lord of the Rings" their richness.
Not only has Tolkien shaped the world of Middle Earth, he has shaped our world as well. In a number of colleges and universities you can study the languages that Tolkien created and become a scholar of them. You can hear some of his languages in the popular movie adaptation of "The Lord of the Rings" directed by Peter Jackson. You can also experience what it's like to explore Middle Earth in The Lord of the Rings Online, a massive multiplayer online game. The developers of LOTRO have gone out of their way to follow the books as they have created and grown their version of Middle Earth and much of Tolkien's histories and languages come into play.
Books can be a very nice way to slip away from the daily grind and have a little adventure. Tolkien's works are one of the best ways to do whether it's reading his books, watching the movies, or playing online. A lot has come out of his work. A lot went into them. I'm just glad that Tolkien decided to share his world with ours!