Henry Creel, better known as One (001) and Vecna, is one of the two main antagonists (alongside the Mind Flayer) of the Stranger Things franchise.
He is the estranged son of Victor and Virginia Creel as well as the younger brother of Alice Creel who gained psychic powers after being transported to the Abyss, where he was possessed by the Mind Flayer. After succumbing to the Flayer's influence which lead to murdering his mother and sister, Henry was captured by Dr. Martin Brenner, becoming the first among the latter's unethical and cruel experimentations. Upon breaking free from Brenner's control and slaughtering the other test subjects, Henry is banished to the Abyss by Eleven, where he reconnects with the Mind Flayer and mutates into his current form.
Years later, he orchestrates the kidnapping of Will Byers, thus setting the events of the show in motion. Seeking to merge Earth and the Abyss, Vecna travels to the Upside Down and goes on a murder spree in the town of Hawkins, allowing himself and the Mind Flayer to start a full-blown invasion of Earth. Because of this, he serves as the archenemy of the Party, particularly towards Eleven, Will Byers and Max Mayfield.