Also known as the Outcast Prince, the Gatekeeper, the Broken Beast
Those who swear themselves to Chernobog swear their souls for all eternity, thinking that it somehow the creature has some means of shielding them from Hell that goes against the natural order of things. In reality, they become vessels to the Gatekeeper, bound by the accords of the Book of Black Passages, sworn to allow entrance to any demon that seeks to enter the world. They become students of the Book and learn the ceremonies of entrance and summoning, each night prepared for the possibility that they might be called upon to allow the spawn of hell entrance into the world. These are acts of the absolute abhorrence and to be found enacting them is punishable by death. For that reason, those that enact these rites are either subtle and careful concealing them, or ruthless against anyone who might find them. They have sworn to Chernobog that they will not allow the whispers of idle tongues from those who do not comprehend the truth of the Gatekeeper's methods. They only even trust their brothers sparingly.
Chernobog is the name associated to the leader of the demonkind that dwells within the bowels of Hell. Some scripture of the Libris Unitas indicates that the gods created Hell first and foremost to act as a prison that could contain Chernobog, and that his eternal torment is to dwell within the eye of the storm of the chaos of Hell and watch his armies suffer in eternal torment for having turned away and acted against the gods.
The Book of Black Passages
Just as worship of Chernobog is heresy, ownership of the Book of Black Passages is a heretical crime punishable by death. The volume contains entire chapters dedicated to the arts of destruction that would best please demonkind and Chernobog, as well as sacrilegious passages that detail the gods as insane, corrupt entities that seek private and perverted pleasures from seeing their followers struggle against and breaking their tenants. It is said to even own the Book erodes the wits of they that possess it, corrupting them in such a matter that their mind becomes fixated on the pursuit of demonic magics and pleasures.