Eberron - Return of the Lich Queen
The Dark Six is a pantheon of six gods cast out of the Sovereign Host during the Schism. Though individual deities are typically singled out and worshiped a few (especially schismatics) worship the whole of the disparate deities. The Dark Six represent evil, destruction and other insidious forces of civilization and nature and members of the pantheon are worshiped by only the most debased of the civilized races and monsters. The holy texts of the Dark Six show them schemeing and plotting against the Sovereign Host at every turn and followers of the Dark Six typically scheme against vassals of the Sovereign Host.
Some believe that the Dark Six were originally Dhakaani gods, that the humans adopted as a counter to the gods of the Sovereign Host, belief in which they brought with them from Sarlona.
The Dark Six consists of the following gods:
* The Keeper (Kol Turrant) – Death and Decay
* The Devourer (Shurkaan) – Wave and Whelm
* The Fury (Szorawai) – Rage and Ruin
* The Mockery (Dol Azur) – Betrayal and Bloodshed
* The Shadow – Magic and Mayhem
* The Traveler – Chaos and Change
For more info: Eberron Wiki