Chors (a.k.a. Churs, Chros, Chers, Xorz, Chorssa, and pretty much any other permutation you can think of) is a rather mysterious god. He was worshipped in pre-Christian Russia and Poland and was probably a god of the sun, although that's not exactly positive.
There are a lot of reasons for Chors to have been a sun god. For one thing, old Slavic texts appear to identify Chors with Apollo. Additionally, the Slovo o pluku Igoreve, a Russian epic, tells how Prince Vsevolod outran the sun, which is referred to as "great Chors." He has been linked to an Iranian sun god, one Khursun, who was also worshipped by the peoples of the central Asian steppes, such as the Scythians and Sarmatians. Chors may also have been descended from this god, a possibility which would explain this otherwise very strange passage in Dialogue of the Three Saints:
"There are two angels of thunder: the Greek Perun and the Jew Chors."
The Dialogue is an apocryphal text and so probably shouldn't be taken too seriously, but it is strange that Chors would be referred to as a thunder god and even stranger by far that he is referred to as being Jewish. This last fact is, I think, only explicable if Khursun was not foreign to Russia and if the author of this piece got his Middle Eastern geography confused. Of course, there are many other possibilities for Chors' origin, ranging from it having been totally a Russian invention, in which case it was descended from the Russian word chorosij, meaning good or kind, to its having been an adaptation of the Greek word "Kruos" (a very rough transliteration), which meant gold.
Chors also may have been some strange mix of indigenous gods that merely wound up confused. Chors is often identified with Dazbog, and it is a possibility that Chors was just the name applied to one particular golden idol of Dazbog that was called by the Greek "Kruos" above, meaning golden. Of course, Chors also had the head of a dog, not unlike the Russian god Veles, as well as horns. There's also the possibility of the god having been stolen from the Ossetians, since they had both a word xorz, meaning good, and their ancestors the Alans had an extremely good god who also went by Xorz.
Wherever he came from and whatever he stood for, Chors was typically invoked by his believers against disease and for luck in hunting. He almost certainly was a sky god, and probably a sun god as well. He was revered by the Polish and the Russians, the latter of which established him as one of their state gods on the hill in front of the palace of the prince of Kiev.
Source: Gray, Louis Herbert. The Mythology of All Races, Volume III. Boston, 1918,
http://www.geocities.com/cas111jd/slavs/slavgods_2.htm