Aurach is an Erinyes, part of the Council of Anarchy in Automata representing the fiends who want to subvert the city.
The other members of the Council are Leggis Scrog and Ravis Corcuncewl.
Planescape Campaign Setting, Sigil and Beyond, page 28
You'll find it with the Indep recruiters.
— Cager slang for It doesn't exist.