Chernobog (Proto-Slavic *čĭrnŭ "black" and *bogŭ "god"), also spelled as Czernobog, Crnobog and Tchernobog is a Slavic deity, whose name means black god, about whom much has been speculated but little can be said definitively. The only historical sources, which are Christian ones, interpret him as a dark, accursed god, but it is questionable how important or malicious he was really considered to be by ancient Slavs. The name is attested only among West Slavic tribes of the 12th century, hence it is speculated that he was not a very important or very old deity. He is the counterpart of Belobog.
One historic source on Slavic mythology mentioning this god is the 12th-century Chronica Slavorum, a work written by German priest Helmold which describes customs and beliefs of several Wendish and Polabian tribes who were still pagans. Helmold wrote that:
The Slavs, too, have a strange delusion. At their feasts and carousals they pass about a bowl over which they utter words, I should not say of consecration but of execration, in the name of the gods — of the good one, as well as of the bad one — professing that all propitious fortune is arranged by the good god, adverse, by the bad god. Hence, also, in their language they call the bad god Diabol, or Zcerneboch, that is, the black god.
Est autem Slavorum mirabilis error; nam in conviviis et compotacionibus suis pateram circumferunt, in quam conferunt, non dicam consecracionis, sed execracionis verba sub nomine deorum, boni scilicet atque mali, omnem prosperam fortunam a bono deo, adversam a malo dirigi profitentes. Unde etiam malum deum lingua sua Diabol sive Zcerneboch, id est nigrum deum, appellant.
On the basis of this inscription, many modern mythographers assumed that, if the evil god was Chernobog, the Black God, then the good god should be Belobog or the White God. However, the name of Belobog is not mentioned by Helmold anywhere in his Chronica, nor is it ever mentioned in any of the historic sources that describe the gods of any Slavic tribe or nation.Svetovid may serve as the opposite god.
A veneration of this deity perhaps survived in folklore of several Slavic nations. In some South Slavic vernaculars, there exists the phrase do zla boga (meaning "to [the] evil god," or perhaps "to [the] evil [of] God"), used as an attribute to express something which is exceedingly negative. No one is really aware of the literal meaning of these words anymore; exclamations such as Ovo je do zla boga dosadno!, To je do zla boga glupo! can be safely translated as "This is devilishly boring!", "That is immensely stupid!" without any actual loss in meaning. This translation is losing actual meaning, because in Slavic language there are common curses used in the middle of the sentence. To je do zla boga glupo! can be translated as "Damn! This is stupid!". It is very similar to the modern Polish expression "do jasnej cholery" literal meaning would be "for shining cholera", but it means the same as ancient "do zła boga". The word Bog ("God"), however, in all Slavic languages today is used as personal name of the Christian God.
He also appears in a number of video games, usually as a villain. In the Bloodseries (where the name is spelled as "Tchernobog") he is depicted not as a person but as an essence of a force that keeps the realities together and must be used by persons incarnating the god. The first game features an incarnation as the main villain, and the second game's plot revolves around the main character Caleb actually being the god. He has also appeared as a recurring demon in the Megami Tensei series.
Chernobog (and Cthulhu) inspired the character of Avoozl the Dark One, master of the antagonists Katrina and Ad-Avis in the Sierra Entertainment adventure-RPG Quest for Glory IV: Shadows of Darkness. He is worshipped by a cult of horrendously mutated priests called "The Chernovy".