Oh PLEASE make that a bookmark! Make him an Arab Pagan that doesn´t give a squat about his subjects, enemies, family, anything! And PLEASE make him extremely difficult to convert. There should be events and decisions UNIQUE to this guy like:
Make Mecca and the Black Stone a tourist attraction
Move the Black Stone... somewhere
Give Independence to Christian vassals
Just give him the same decisions and events you would give Emperor Nero or Caligula!
Edit: These events and decisions would have to be impossible for the AI to implement?