Believer is a mercenary who speaks strangely, and acts like he is better than anyone else, except for 'them.' He never speaks about who 'they' are, but it is believed that he refers to a ghost that possessed him. He has a throwing knife which has strange properties, marking anyone it hits. If that person dies while marked, they will become a spirit and will serve 'them.' He also knows who 'they' are, almost to a personal level, based off of interviews.
His real name was taken by 'them.'