Henry Creel/One/Vecna is not only the big bad in "Stranger Things" Season 4, but he's also been a looming presence throughout the whole series. Despite the fact that nobody would invite Vecna to dinner, the sweet-as-can-be actor below the makeup, Jamie Campbell Bowers, would make anyone's guest list.
More commonly known as "Papa" to Eleven, Dr. Brenner is inarguably the most detestable character in "Stranger Things." While most human characters in the series are not outright villains, there's no doubt that Dr. Brenner's intentions are wholly malicious.