From HandWiki

In Ugrian mythology, Heini-iki, also referred to as Kul-iki, is the god of the Underworld and of the spirits of sickness.[1] He is opposite in nature to his brother Numi-Torum, the heavenly god. He can appear in the shape of a dog or cat, or sometimes as a fog that hides a person from their guardian spirit. The Khanties of the Surgut area described him as black in color. Animal sacrifices to him were also to be black in color.[1] These sacrifices were to prevent illness among the people. His name was not to be spoken, especially in the presence of a sick or dying person.[2]