The Doctor of the Fatui always acted cold and egotistical, to the point where anyone who met him wondered if this man was just straight up insane or if something had made him this way

To be fair — maybe it was a bit of both, as he worked away in his lab, his back turned to you, refusing to acknowledge the haunting presence of your ghostly body, the ghost of the person who had once been his most treasured lover centuries ago which was now just a whisper amongst the living, haunting him.