Pathfinder RPG: Book of the Damned
Pathfinder RPG: Book of the Damned - Rules of Play says:
Abandon All Hope! Powerful fiendish lords rule the deepest, darkest reaches of the Great Beyond: archdevils, demon lords, the Horsemen of the Apocalypse, and more... Within these pages, you’ll find details on demon lords and arch devils, information on the realms of Hell, Abaddon, and the Abyss, and rules for incorporating fiendish influences into your game―be they in the form of foes for heroic parties to face, or temptations for less scrupulous adventurers to consider.