Dazbog, also known as Dazdbog, was a sun god of pre-Christian Russia. His name more than likely means "the Giving God," although at times other appellations are applied to him as well, most notably "Czar Sun" and "Son of Svarog." These last two names are the basis of the modern assumption that he was a sun god. although the first name is pretty well self-evident, the second is a reference to Svarog, another Slavic god who was notable for turning out sons who were then identified with the sun (e.g. Svarazic of the Elbe Slavs, who is also called "Son of Svarog"). Also, in older Russian translations of Greek classics, the name of the Greek god Helios, the embodiment of the sun, was translated as Dazbog.
As was the practice of many ancient Slavic people, the Russians traced their ancestry in legend, most notably in the epic Slovo o pluku Igoreve. In that piece, the Russian prince Vladimir refers to himself and the rest of Russia as being grandchildren of Dazbog. The same prince Vladimir, outside of legend, set a statue of Dazbog on the hill in front of his palace with most of the other gods worshipped in that time.
After the advent of Christianity in Slavic society, Dazbog's role appears to have changed in a manner rather unusual among European pagan deities. Rather than being coopted into Orthodox Christianity as so many other deities and holidays were, Dazbog became an explicitly anti-Christian figure. He is in fact contrasted with the Christian god in the Serbian fairy tale of Dabog, a.k.a. Dajbog. No matter which way the name is spelled, Dazbog is the deity pictured as being in opposition to God: "Dabog, the Czar, was on earth, and the Lord God was in heaven." The source I'm reading suggests that this passage was meant to put Dazbog into a position not unlike that of the Judeo-Christian devil in that he was given Czarship over the earth while God held sway in heaven. I won't necessarily say that I agree there, but I will repeat what they said (and all the frankly meager evidence they gave) and let you make up your own mind.
Source: Gray, Louis Herbert. The Mythology of All Races, Volume III. Boston, 1918.