Chernobog (Proto-Slavic *čĭrnŭ 'black' and *bogŭ "god"), also spelled as Chernabog, Czernobog, Chornoboh, 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. Older scholarship assumed him to be 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.
Chernobog has made appearances in various media. As Chernabog, he features in the "Night on Bald Mountain" sequence in Disney'sFantasia (1940), as a gigantic black gargoyle like creature who summons other ghosts and demons. In an interview, Walt Disney referred to him as Satan himself.Deems Taylor likewise refers to him as such in the film.
Chernobog appeared in the Marvel Comics series Thor. He was slain by a villain, a powerful god-killer. Chernobog's flying steed helps Thor fight back. 
Chernobog is mentioned in several books in the Kate Daniels series by Ilona Andrews. Specifically the Russian Volvh dedicated to Chernobog.