Necronomicon?
Its an book of Dark Magic in the world of Daventry according to the King's Quest Companion. It was written by someone known as the "mad Arab Abdul Alhazred". It contains knowledge so terrible that a mere glance at the illustrations and illuminations in the text drives many to madness.
The book is also known as the Al Azif.
Both Abdul Alhazred, and Necronomicon are refrefrences a character and book, originally created by H.P. Lovecraft in one of his stories. Interesting trivia if anyone is interested where Roberta Williams got the name for the character.
In Lovecraft lore its full of dark rituals and spells related to Old Gods, and from what I remember looking at its pages may cause the reader to go mad(hence the explanation above from the companion).
You might remember a similar book in QFG4.
Its a point to ponder if the Mad Arab mentioned in King's Quest Companion, is the same Abdul Alhazred from KQ6, or did his parents just name him after the other guy.
In anycase the Abdul Alhazred we are most acquainted seems to be more of the political dignitary than a wizard. If he does know alot of magic, or at least a few "parlor tricks", he is probably the type not to flaunt it, and get his hands dirty, but rather uses others to do his work for him.
Also its interesting point that Companion makes about Abdul's and Shadrack's plans for the Green Isles;
But it seems the plans for that little kingdom of yours are coming along, you seem to have the destruction of the kingdom well in hand.
It appears Genocide may have been part of black cloak's ultimate plans for the nation.