The position of Rollmaster is one of the oldest House positions in the Dark Brotherhood along with Quaestor and Aedile. The Rollmaster, before the concept of the database, was charged with keeping an accuarate roll of the House's membership. They would sort them by rank and then by Order and save it to a Rich Text File (.rtf), which would be submitted to the Master At Arms for his record keeping.
The position became unnecessary upon the creation of the database system by the then serving Master At Arms, Thedek. The position has been kept by some Clans and Houses as an auxillary command position but for the most part it is no longer required.