Who is Grand Inquisitor John Domenico Mustafa from The Rise of Endymion and what is their importance?

The Grand Inquisitor, John Domenico Mustafa, is in charge of the Inquisition. His devotion to the Church is in large part a response to the power it gives him over others. Mustafa, however, is deceived as to the Church's real motives and relationship with the Core. Although he is described as a dishonest and immoral man, Mustafa is nonetheless mortified when these facts are revealed.