Taken from Wikipedia.org: "In the Sioux tradition, Wakan Tanka is the term for the "sacred" or the "divine". It is often translated as "The Great Spirit". However, its meaning is closer to "Great Mystery" as Lakota spirituality is not monotheistic. Before the attempted conversion to Christianity, Wakȟáŋ Tȟáŋka was used to refer an organization of sacred entities whose ways were mysterious; thus the meaning of "the Great Mystery". It is typically understood as the power or the sacredness which resides in everything, similar to many animistic and pantheistic notions. This term describes every creature and object as wakȟáŋ ("holy") or having aspects that are wakȟáŋ."
I have a friend who is part Cherokee and sits on a council, and he tells me that they have a Wanka Tanka as well. He described the diety as Great Spirit or Great Protector.
The Spirit would take the form of an animal, to investigate the happenings in a certain area. If it was a mountainous region, the Spirit would become a mountain lion. If it was open prairie, the Spirit would become an eagle. Woodlands would be a wolf, deep forest would be a bear, lakes would be a fish. The Spirit always chose the top form it could, which is why it would be a wolf instead of a squirrel, or a muskellunge instead of a bluegill.
The Spirit would patrol the area it was in, in an attempt to level the playing field. It was seen as the balancing force among nature. Many people claim to have seen a giant black bear (muckwah) in the woods that shows no fear. Others talk of a giant fish that broke their lines, or snapped their poles, or seemed longer than their boat. From what I've been told, the Spirit can never be captured, never be killed, and is never witnessed by two or more people at the same time. It keeps itself protected this way, because if a dozen people saw a 500lb black bear in the woods, the hunt for it would be on and more damage would be caused. Lakes would be overfished in an attempt to catch a 12 foot muskie, birds would be shot from the sky in hopes of catching the elusive eagle, and so forth.