On September 21, 1937, George Allen and Unwin published The Hobbit, or There and Back Again, by J.R.R. Tolkien, in an edition of 1,500 copies for the British market. It had ten black and white illustrations, maps and a dust jacket, all by Tolkien himself. The British printing sold out by December and was followed by three more printings before the end of the year.
It had been written in the early 1930s, mostly for his own children, and it had circulated in typescript. One copy reached Susan Dagnall, a former student of Tolkien's who worked for the publisher, who showed it to Stanley Unwin, who gave it to his son Rayner, then 10, to read. Rayner's report on it is why the book was published, and the fee was 25 pounds for the reading.
Tolkien was no children's writer. He was 45, a professor of Anglo-Saxon at Oxford, a philologist who had worked on Beowulf and on the Middle English Ancrene Wisse, and he had been building a private mythology since 1917, with its own languages, history and cosmology. That material, which became the Silmarillion, was not published in his lifetime. The Hobbit started as a separate thing: a story about a small man who leaves home and comes back richer, and it borrowed the name of the dragon from the Old Norse and the idea of the riddle contest from the same place.
The sequel changed it. Unwin asked for another hobbit book in November 1937, and Tolkien began one, and by the end of 1938 he had written the chapter that would be A Long-Expected Party. What he was writing had stopped being a children's book, and he knew it. It took twelve years, with long interruptions, a war, and a move to Merton College, and it appeared in three volumes between July 1954 and October 1955.
The influence is hard to overstate and easy to exaggerate. Tolkien did not invent the quest, the wizard or the dragon, but he did invent the consistency: a world with languages worked out in grammar and vocabulary, history in layers, and a map that could be checked, and that standard is what later fantasy has been measured against. They sold 150 million copies. Tolkien died in 1973, and the Silmarillion was published posthumously in 1977.