House Dimir

House Dimir is Ravnica’s dark secret: behind a facade of respectable messengers and reporters lurks an association of spies and assassins whose existence is barely suspected by the populace at large. Secrecy is both House Dimir’s best weapon and its best defense, and much of the guild’s work is hidden even from other members. Dimir agents leave no trace of their covert activities, warping the memories of witnesses to their crimes and even wiping their own minds to remove any evidence of their completed assignments.
The first guildmaster of House Dimir was a vampire named Szadek, whose organization agreed to serve as Ravnica’s couriers, information brokers, and librarians. But Szadek also used his guild’s expertise at gathering information to build a vast spy network, and before long, the secret operations of the guild vastly outweighed its overt ones. Eventually the guild disappeared into the shadows, and most Ravnicans came to doubt its existence. An immortal entity, Szadek ruled the guild for ten thousand years until he was arrested and killed in the turmoil of the Decamillennial Celebration.