The Demon Bear appeared in the first book, Wolf Brother as the primary antagonist. Originally a young wild bear it was caught when Hord of the Raven Clan helped a "crippled wanderer" to capture it. At the time Hord did not know that it was meant to be turned into a demon nor that the crippled wanderer was in fact Tenris, soon to be Mage of the Seal Clan, and a hidden Soul Eater.
The later put an Elemental demon into the body of the bear using a piece of the Fire Opal. With immense power and hatred at its disposal the demon bear grew stronger and stronger, reaping a terrible vengeance on Red Deer Clan (whom Hord and Tenris had been staying with). By the time the Deep Forest Clan were able to drive the abomination away and Hord realised the mistake he had made, Tenris had disappeared.
The Demon Bear made its way into the Open Forest, where it eventually tracked down and attacked young Torak and his Father. Whilst the initial attack brought no victims the bear soon returned and managed to kill the later, whereupon it went on a murderous rampage slaying innocent animals and bringing terror and death to the clans.
At the end of the book Torak and Wolf successfully destroyed the bear by bringing the three pieces of the Nanuak to please the World Spirit to gain his help. As the bear attacked Torak and an intervening Hord, Wolf took the pieces to the top of the Mountain of the World Spirit and the World Spirit sent an avalanche which destroyed the demon bear and killed Hord.