Billy Hargrove

Billy Hargrove, portrayed by Dacre Montgomery, was a main character and antagonist in Stranger Things, having been introduced in the second season. Originating from California, he moved to Hawkins, Indiana in 1984, where he attended Hawkins High School until his graduation.
He was the older step-brother of Max Mayfield, who he often mistreated among others. Eventually, he became under the possession of the Mind Flayer, who used him as a vessel and also as a tool to gather civilians of Hawkins, to create a larger physical vessel to host the Mind Flayer; the Spider Monster. Unlike the other Flayed, he was never integrated into the Monster's body and was granted a degree of superhuman ability while acting under the Mind Flayer's command, but his actions were still mostly under the direct control of the Flayer.
During a moment in which Billy dragged Eleven toward the Mind Flayer and was about to give her up to it, she was able to reach his humanity by reminding Billy of the boy he was. The boy that existed before his mother's departure, which left him to be raised by an abusive father, eventually turning him into the bully he became. Deciding to make a change, Billy physically held back the Monster, who killed him by stabbing him in the chest. In his final words, he apologized to his stepsister. His death was covered up by the government, as part of the Starcourt Mall's fire.