Demonomicon of Iggwilv

The Demonomicon of Iggwilv is a text attributed to the witch Iggwilv of Oerth. During her affair with the Demon Prince Graz'zt, she collected a large number of the true names of demons and a wealth of fiendish lore, all of which she recorded in the Demonomicon. After her defeat at the hands of the Wizard Mordenkainen, the Demonomicon went missing, and its whereabouts are unknown. It has supposedly been seen on Tol during one of Mordenkainen's otherworldly visits, but, happily, hasn't been seen in at least five-hundred years.