Billy Hargrove

Billy Hargrove, portrayed by Dacre Montgomery, is a major antagonist in Stranger Things, known as Max Mayfield's abusive and aggressive stepbrother who becomes a host for the Mind Flayer in Season 3, ultimately redeeming himself by sacrificing his life to save Eleven. His violent behavior stems from abuse by his father, leading to a charismatic but troubled "bad boy" persona that evolves into a tragic figure.