Crnobog also known as Crnoglav (Black Head) is the god of darkness and the ruler of the world of the dead. He is black which helps him blend in with his dark and eerie underground domain. He is the only one who completely opposes the gods that like human kind and he is the only one that is entirely evil.
Completely evil gods are as rare as completely good ones. With that in mind we can conclude that ancient gods can be divided into good ones and evil ones only by human moral norms and criteria, which in the eyes of all powerful gods hold little to no value.
All kinds of rituals in the glory of Crnobog are recorded in history, most of them featuring women. The ceremonies took place at night under the light of torches or big bonfires. Women danced until they fell into trance, holding snakes as offerings to Crnobog.
In Slav tradition a sacrificial goblet was drank from at feasts, both in the name of good and evil goods because they believed that every kind of luck must come from good gods and that every kind of misfortune comes from evil gods. Even though Crnobog is sometimes equalled with the devil it is clear that he is not just some evil demon or demigod but a full-fledged blood god of all Slavs, the greatest god of the underworld and of all evils that can take infinite number of forms. Sacrifices were made, wine was drank in his name, just like in the name of any other god. He had his cult too, cult respectable as a cult of any other god.
Thus, the Slavs considered Crnobog’s role to be necessary which made him equal to all other gods in the pantheon.
Crnobog and Belobog
It is presumed that on the other side of the scales from Crnobog stands Belobog (White God) but unfortunately little is known about Belobog. Sometimes Belobog is also called Bjelun. Maybe it’s actually Perun hidden behind this name because of his white beard and his sense of justice that is contrary to evil.