Vecna

His real name is Henry Creel, however since the fight with eleven his face become unrecognizable and his true name faded away leaving him with a pseudonym Vecna. He moved from our world to the world that is called Upside Down. That world is mirrored version of our world except it is dark, cold and filled with evil creatures that follow Vecna's commands. He is gaining strenght in that world so he can conquer our world. Instead of clothes he is covered in moving veins which sometimes get a little snappy.