Necronomicon

A fictional medieval grimoire, originating from the works of H.P. Lovecraft, belived to have been written by th Mad Arab, Abdul Alhazred. The book suposedly contains information on the Old Ones and magical spells to summon or ward them off, create zombies and so on. Many believe the book to be real, despite Lovecraft's assertion to the contrary and several copies have surfaced, for example the Simon Necronomicon, which mixes the original Cthulhu Mythos with Sumerian mythology and medieval magical practices (like the Salomon Key).

Both the sci-fi and fantasy genre often reference the Necronomicon, usually in a humorous way (Monsternomicon, Necrocomicon, etc). The horror genre usually takes the book as it is, since Lovecraft's creations have become a sort of meme, shared by the collective.