The subject of this study is the evolution of the image of the bear among the Eastern Slavs between the tenth and seventeenth centuries. The authors maintain that totemic ideas about bears as creatures that escort the souls of the deceased to the kingdom of the dead began to spread in the East Slavic lands only from the mid-tenth century. Such ideas were influenced by the beliefs and cults of the neighbouring Finno-Ugric and Baltic tribes and were not characteristic of traditional East Slavic paganism. Based on ancient Russian writings and archaeological excavations into ancient pagan sanctuaries, the authors outline the origin and formation of the myth of the supernatural ancestor bear, the protector of the human race, in all East Slavic lands. With the help of archaeological and zoological materials from the excavations of Russian settlements from the pre-Mongol era, as well as several ancient Russian written documents, the authors determine the period of transformation in the folk mythological consciousness of the Eastern Slavs of the mythological image of the bear from the ruler of destinies and guide in the kingdom of the dead into a forest demon. This paper emphasises that the myth of the supernatural ancestor bear gave rise to the custom of taking trained bears around Russian cities to rid them of evil spirits, as well as folk divination. The authors conclude that in the minds of these ancestors, the image of the bear went through several stages – from the idea of the bear as a tribal totem to the image of a benevolent spirit, a protector of people from evil spirits. The ancient pagan ideas about the bear as a deity remained part of the worldview of the East Slavic peoples until the early twentieth century, finding their reflection in folk fairytales, legends, and traditions.