De Camp, L. Sprague, Catherine Crook de Camp, and Jane Whittington Griffin. Dark Valley Destiny: The Life of Robert E. Howard. New York: Bluejay Books, 1983. This is the standard biography. It includes a good analysis of The Hour of the Dragon.

Edwards, Malcolm J. "Robert E. Howard." In The Science Fiction Encyclopedia, edited by Peter Nicholls, et al. Garden City, NY: Dolphin Books (Doubleday), 1979. A good summary of Howard's works, emphasizing his Conan stories.

Howard, Robert E. "The Hyborian Age."

In Red Nails, edited by Karl Edward Wagner. New York: Putnam's, 1977.

Howard describes the history of his imaginary Hyborian Age.

Wagner, Karl Edward. "Foreword" and "Afterword." In The Hour of the Dragon, by Robert E. Howard. New York: Putnam's, 1977. This is an authoritative edition of the novel, restoring it to its original published form. Wagner provides a good history of the novel's creation and...