August William Derleth was an American writer and anthologist. He was the first book publisher of the writings of H. P. Lovecraft. He made contributions to the Cthulhu Mythos and the cosmic horror genre and helped found the publisher Arkham House. Derleth was also 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. Notably, he created the fictional detective Solar Pons, a pastiche of Arthur Conan Doyle's Sherlock Holmes.

The Cthulhu Mythos is a mythopoeia and a shared fictional universe, originating in the works of American horror writer H. P. Lovecraft. The term was coined by August Derleth, a contemporary correspondent and protégé of Lovecraft, to identify the settings, tropes, and lore that were employed by Lovecraft and his literary successors. The name "Cthulhu" derives from the central creature in Lovecraft's seminal short story "The Call of Cthulhu", first published in the pulp magazine Weird Tales in 1928.