The Stranger Things Monsters

Eleven is the reason the monster, the Demogorgon, exists.  It's the result of the torture placed on her due to Dr. Brenner's experiments.   In the Dungeons & Dragons fantasy role-playing game, Demogorgon is a powerful demon prince. He is known as the Prince of Demons, a self-proclaimed title he holds by virtue of his power and influence, which, in turn, is a title acknowledged by both mortals and his fellow demons. Demogorgon was also named as one of the greatest villains in D&D history by the final print issue of Dragon.