The history of modern fantasy books.

In the 12th, and 13th century, fantasy was mostly King Arthur. There are now more than 200 copies of Geoffrey of Mounmoth's book of about 1140 A.D. which introduced most of what is now in every fantasy story about Arthur. Like for instance Merlin and the company of valiant knights.  Only the Bible has more surviving copies from books that old.

As time marched on, very little fantasy was written. Only the odd book here and there. In modern bookstores, there were no reserved "Fantasy" sections until 1954 when Tolkien's Lord of the Rings was produced. It was a phenomenal success! A new popular genre was suddenly born.

Fantasy books were now no longer odd or unusual. Lester Del Rey (himself a SciFi author) became the "fantasy" editor of Ballantine books. His wife July-Lynn was the Sci Fi editor at Ballantine. Lester Del Rey used Tolkien's works as a model of what  fantasy stories Ballantine's would publish and what they would not. Based on what he knew would sell and what would not. (Fantasy would be positive, no strong violence nor sex, not dark).

Lester and Judy-Lynn

Very much later, the counter revolution against Del Rey (on the left) was led by the shorter man next to him (George R.R. Martin). Tolkien and his created character, of course on the right.