The Dark Brotherhood is an organisation of professional assassins who worship Sithis and the Night Mother. The Dark Brotherhood can be called with a ritual called The Black Sacrament. Once, the Dark Brotherhood was bound to the Five Tenets, which set the rules for being in the Brotherhood, but they were abandoned. Also, the Dark Brotherhood shrunk very much in the last 200 years, and the mission of the player is it to help the Brotherhood to its old fame.