Sisyphus is a figure in both Greek and Roman Mythology.
In life, Sisyphus was a King, and was labelled the ‘craftiest of all men’ by Homer.
Before he died, he ordered his wife to give him an improper burial, none of the rites or libations that were sacred at the time were to be performed on him.
In doing this, when he went down to the Underworld, Sisyphus persuaded Persephone that his wife had not buried him properly, and she granted him a day to go back to Earth and remedy this, however upon learning his plan and his trickery he was punished by the Gods to roll a boulder up a hill, in Tartarus, only to watch the boulder roll back down when he had finally reached the top. This same event took place every day, for eternity.
Sisyphus’ main flaw was his hubris, like that of many heroes in Greek Mythology. He believed his intelligence was on par with Zeus himself, so this is why the frustrating and pointless task is perfect as a punishment for him.
Thus it came to pass that pointless and/or interminable activities are sometimes described as Sisyphean.