Nyarlathotep is a fictional character created by H. P. Lovecraft. The character is a malign deity in the Cthulhu Mythos, a shared universe. First appearing in Lovecraft's 1920 prose poem "Nyarlathotep", he was later mentioned in other works by Lovecraft and by other writers. Later, writers describe him as one of the Outer Gods, an alien pantheon.

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.