Rule-of-Three

Rule-of-Three is a cambion working with Graz'zt in a plan to unite the Baatezu, Tanar'ri, and Yugoloths.

Rule-of-Three is just about the most knowledgeable source on the Abyss available. He dwells on Azzagrat in the city of Zelatar or in Sigil. He is allied with Graz'zt, and knows much about the Abyssal Realms. When in Azzagrat, he stays in the back room of an inn called the Golden Opportunity. People searching for information from him can easily access it, for a three-pronged price, such as precious metals of three different types or three magic items.

Rule-of-Three is the mastermind behind the plan for which he is named, a uniting of Tanar'ri, Yugoloth, and Baatezu to take over the upper planes.