Duke
From Emperor's Hammer Encyclopaedia Imperia
Very few members of the Directorate are likely to achieve this rank, as it is reserved solely for Grand Moffs and truly exceptional Deputy Grand Moffs. Dukes are very well-respected members of the New Order, and are considered the crème of Imperial society. The Grand Moff is bestowed this title (of the Aurora System) upon their ascension to the Office, and the Fleet Commander is also granted the bestowment of the title "Duke of the Emperor's Hammer Territories". A member who is granted this title may use the title "Duke" or "Duchess" in formal occasions, and are permitted the privilege of representing a specific location within the Emperor's Hammer.
Grand Moff, Duke John Doe of Aurora
Grand Moff, Duchess Jane Doe of Aurora