John Domenico Mustafa is the Grand Inquisitor of the Holy Office, he is among the most powerful Cardinals and is not a close ally of Lourdusamy's faction. He personally investigates the Shrike's massacres on Mars toward the beginning of The Rise of Endymion novel, and is also the Church's direct representative throughout the search for Aenea on T'ien Shan.
His personal assistant is Father Farrel.
He confronts TechnoCore forces twice during the novel, and is fatally wounded by Nemes the first time and murdered by Albedo the next.