Lords of the Outer Realms
Beyond the Prime Material Plane, or Mortal Realm, as it is sometimes known, lie many other dimensions, or Outer Realms. Every god has his or her own plane from which they can influence the Mortal Realm.
In addition to the realms of the gods are nine realms based on the nine moral alignments. When a spirit leaves the Mortal Realm, and is not claimed by a god to go to that god’s realm, the spirit instead is drawn naturally to the realm to which it is most closely aligned. Each realm is ruled by one or more Lords. Though a Lord’s power is vast, it is not absolute, and they can be overthrown or deposed by someone more powerful.
The gods never directly interfere with or appear in the Moral Realm, and only affect it through their agents. The Lords are under no such restriction, and can be summoned from their Realms by sufficiently powerful magic. They cannot appear of their own will; they must be called, and they must return when the magic that calls them ends.
The fact that the Lords exist is fairly widely known after the incident two hundred years ago when Mammon, the Lord of the Lawful Evil plane and embodiment of the sin of greed, walked the Mortal Plane as a human for some time. However, the ability to summon them is all but gone from the world, and anybody who does have the ability is keeping silent about it.
There is no set list of shared powers among the Lords; each is unique. For example, Mammon can, as an ability unique to him, compel any Lawful Evil Devil to do his bidding without limit or restriction. However, the Chaotic Neutral Plane’s Lord is a title shared by two entities who have no inherent magical powers or abilities at all; they rule through unstoppable physical strength, cunning, and the use of magical artifacts.