Belobog, Bilobog, Belbog, Bialbog, Byelobog, Bielobog, Belun or Bylun, Bielboh or Bialun (Belarusian: Белбог, Бялун) (all names meaning White God) is a reconstructed Slavic deity of light and Sun, the counterpart of dark and cursed Chernobog (Black God). It is uncertain whether such a deity was ever worshipped by polytheist Slavs, as there are no reliable historic records which mention this name. While in the past a great deal of scholars studying Slavic mythology took the dualism of Belobog and Czernobog for granted, modern research of the matter makes this theory very hard to maintain.
In the later half of the 12th century, the German priest Helmold described, in his work Chronica Slavorum, beliefs and customs of several West Slavic tribes who were still polytheists at the time. Amongst other things, he stated that: The Slavs, they say, have one peculiar custom: during feasts, they pass a goblet amongst them in circle, for purpose not to praise, but rather to curse in the names of gods, good and evil, for every good thing praising a good god, and for every bad thing cursing an evil god. This god of woe in their language is called Diabolous (*in Latin) or Zherneboh, meaning black god.
On the basis of this inscription, many modern mythographers assumed that, if the evil god was Czernobog, 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. Additionally, the inscription quoted above is more likely Helmold's own interpretation than an accurate description of Slavic pre-monotheistic beliefs: Helmold, being German, did not know the language of Slavs, and being a Christian priest, did not have much, if any, contact with the polytheists themselves; while his information about Slavic mythology is valuable, one would be wise not to take them for granted.
Another clue for existence of Belobog is a number of toponyms in Slavic countries which have that name. They include Bělbožice in Czech Republic, Bilobozhnytsia in Ukraine, and Bialoboze recorded in Poland. Sometimes the toponyms are paired with those having the name Czernobog as in the case of hills Bileboh and Czorneboh near Bautzen in Sorbia, and of the Czech Bělbožice which is likewise paired with Černíkovice. This was one of the arguments for the dualism theory.