Chernobog (also spelled Crnobog, Czernobog, Černobog or Zernebog, each name meaning Black God) is a mysterious Slavic deity of whom much has been speculated but little can be said. It is indicated he was a dark and cursed god, but it is questionable how important he really was to 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.

A veneration of this deity perhaps survived in folklore of several Slavic nations. In some South Slavic vernaculars, there exists an interesting phrase do zla boga (meaning "to [the] evil god," or perhaps "to [the] evil [of] God," which may denote ownership rather than some dark attribute), 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. The word Bog ("God"), however, in all Slavic languages today is used as personal name of the Christian God, who, according to Christian beliefs, is not evil; thus, the expression zli bog, "evil god", could be a relic from pagan antiquity. If we assume that Crnobog indeed was an evil and dark god of the ancient Slavs (or perhaps merely an evil aspect of some other deity), we may conjecture this expression was some ancient curse invoking him.