As a punishment from the gods for his trickery, Sisyphus was sentenced to the deepest portion of Hades were he was compelled to roll a huge rock up a steep hill, but before he could reach the top of the hill, the rock would always roll back down again, forcing him to begin again. Occasionally, Sisyphus was employeed to guard one of the Gates of Hades.

SOURCE(S): Zork:Grand Inquisitor