Necronomicon
According to Lovecraft, the Necronomicon was written in the eighth century by a crazy Arabian man named Abdul Alhazred. Alhazred (who was also fictional) practiced evil magic.  He assembled a collection of evil spells into a manuscript (a book with loose pages and no cover) which he called Al Azif. Lovecraft said this as an Arabian phrase for a scary sound, like a scream.  Later, the original manuscript was translated into Greek.  It was given the title Necronomicon.  Olaus Wormius (a real person) then translated the Greek version into Latin.  John Dee (also real) translated the Necronomicon into English.  Lovecraft liked to mix in real people and places in his fiction.  This made the stories seem more real.  Some people were fooled into thinking what he wrote was true.