The Demon Bear is a villain in the Marvel universe and an enemy towards the New Mutants - it has many similarities to Llan and Adversary, both of which are nigh-omnipotent demonic entities and enemies of mutant-related heroes.
The origins of the Demon Bear is unknown. This creature was originally an entity who use to haunt the dreams of Danielle Moonstar, by threatening her that he would find and kill her. He was seemingly the one responsible for the deaths of her parents, William and Margaret Lonestar.
X-Men Film Series
Demon Bear will appear as the main antagonist of 2018 X-Men film, New Mutants.