Vecna.

About Vecna

Henry Creel, commonly known as Vecna and also as One or Mr. Whatsit, is a fictional character and the main antagonist of the Netflix science fiction horror television series Stranger Things. He is portrayed by Jamie Campbell Bower. The character was introduced in the fourth season as a malevolent being from the Upside Down, a mirroring alternate dimension, that haunts his victims with horrifying visions of their past traumas before killing them in a sadistic, brutal manner. As the fourth season progresses, he is ultimately revealed to be the alpha of the Upside Down and the mastermind behind all of the events that previously terrorized the town of Hawkins, beginning with the disappearance of Will Byers, revealing himself to be a vengeful misanthrope bent on bringing on human extinction, by aiding the Mind Flayer in its goals.