August William Derleth (February 24, 1909 – July 4, 1971) was an American writer and anthologist. Though best remembered as the first book publisher of the writings of H. P. Lovecraft, and for his own contributions to the Cthulhu Mythos and the cosmic horror genre, as well as his founding of the publisher Arkham House (which did much to bring supernatural fiction into print in hardcover in the US that had only been readily available in the UK), Derleth was a leading American regional writer of his day, as well as prolific in several other genres, including historical fiction, poetry, detective fiction, science fiction, and biography.

A 1938 Guggenheim Fellow, Derleth considered his most serious work to be the ambitious Sac Prairie Saga, a series of fiction, historical fiction, poetry, and non-fiction naturalist works designed to memorialize life in the Wisconsin he knew. Derleth can also be considered a pioneering naturalist and conservationist in his writing.