Who is The Bishop of X from The 120 Days of Sodom and Other Writings and what is their importance?

The Bishop of X is the Duc de Blangis's brother, as well as one of the "four friends". He is forty-five-years-old, nervous, and delicately built. He was appointed the guardian of two, young children and their inheritance, both of whom he had killed for their fortune. The Bishop of X also has a fondness for sodomy.