Mercer is assisted in the running of the Guild by his right-hand man Brynjolf and the treasurer Delvin Mallory. The current head of the Guild is Mercer Frey, his predecessor Gallus Desidenius was killed while attending a meeting. Some within the Guild believe that the run of bad luck has been brought on by a curse. The Thieves' Guild has fallen on hard times recently and has been in sharp decline. But it is likely that it was founded around the same time as the city of Riften was.
It is unknown when the Guild was founded.
There is a secret entrance to the hideout located in the Riften graveyard, inside the only large tomb in the place. They can be found in the Ratway beneath Riften, and are based in the Ragged Flagon, a tavern hidden in the Ratway run by the thieves. The Thieves' Guild is a faction the Dragonborn can join in Skyrim.
