Who is Baba Yaga from Enchantment and what is their importance?

Baba Yaga is a witch, and the widow of King Brat, who was pushed out of Kiev and forced to rule a smaller kingdom. After his death, Baba Yaga claimed his lands by the widows-right, something that does not exist but many are too afraid to protest. She then married Winter Bear, the god of winter, who has great powers. When the bond between them is broken, however, all the spells Baba Yaga has created with his powers are undone.