Traitor

This is the most common role on the Mafia side that isn't actually in the Mafia family. There are several variations of this role.

In small games, the Traitor most commonly knows who is in the Mafia, but the Mafia do not know who the Traitor is. The Traitor works, through his or her Vote, to keep the Mafia from getting Lynched.

Another variation is the Mafia Cop. This version does not know who is in the Mafia, but can investigate once each Night, like a normal Cop, to help the Mafia in lynching. The original Mafia Cop was in the Mafia itself, but this role was simply a more powerful Mafia member, rather than a separate role.

In a third variation, sometimes used in conjunction with the second, the Mafia can choose at any time in the game to recruit their Traitor. Before this time, the Traitor appears innocent to Cops, and/or has investigative abilities. Once recruited, the Traitor becomes a normal Mafia member.

In recent games, this role is more commonly known as a Mafia Spy.