David Day is the author of five important works about J.R.R. Tolkien's world. A Guide to Tolkien's World: A Bestiary and A Guide to Tolkien are two books by Tolkien. These two publications, along with Tolkien: The Illustrated Encyclopedia, have been translated into sixteen languages and sold over two million copies. Day, a Canadian who lives in Toronto, has written over thirty books for adults and children on mythology, history, fantasy, fiction, and poetry.