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.
While the Demon Bear's origins are currently unknown and not even its real name has been mentioned, it is known that the bear used to reside in Danielle Moonstar's nightmares, and Danielle would always be extremely scared of the bear, as the bear had supposedly murdered both of Danielle's parents.
Instead of confronting the demonic entity, Danielle would at first think that the bear was only part of her imagination as a nightmare and that Professor X would have started it when he was possessed by the Brood Queen and started trying to implant Brood Embryos inside of his students. She also thought for a while that the bear was a creation of her powers.
Whatever thought she had about the bear, she would always hide them away from her team, and never even mention the existence of the bear, no matter how much the bear would negatively influence her life.
The bear once confronted Danielle as a phantom and told her that it was going to kill her. This motivated Danielle to stand up and confront the bear and started training for the battle.
During the battle, Danielle was overconfident after training a lot, and her overconfidence ultimately leads to her downfall in the battle. The demon bear savagely tore Danielle down, severely hurting Danielle's spine in the process. This could have killed Danielle, but to her delight, Wolfsbane has a telepathic connection to her and therefore found out about what happened to Danielle.
Wolfsbane and her teammates in the New Mutants team instantly rushed Danielle to the Mid-County Medical Center in order to save her. Despite winning the battle, the bear was definitely not done with Danielle. It managed to find out where Danielle was and ran into the hospital as fast as it possibly could.
When defeating Danielle, it wanted to possess Danielle's soul. The bear transported the team of New Mutants to what could possibly be its own dimension, the Badlands, where they had their final battle.
The bear didn't manage to possess Danielle's soul, but instead Sharon Friedlander and Tom Corsi, both of which it transformed into native American warriors that were under control of the bear. Magik killed the bear with her sword, and once the bear died, both of Danielle's parents came back. Instead of what Danielle originally thought the bear did to them, killed them, it turned out that the bear actually enslaved them instead.
- The Demon Bear will appear as the main antagonist of the 2018 horror movie, The New Mutants.