It was Zeus who condemned Sisyphus to roll a boulder up a hill for all eternity. Sisyphus was super smart, but super evil too. He did all kinds of bad things like impregnating his niece in a plot to kill his brother. Some historians said that he also killed people (guests and travelers). Plus, he actually betrayed the secrets of the gods. As his ultimate punishment for his crimes, Zeus required and caused Sisyphus to endlessly roll a huge boulder up a steep hill.

It was Zeus who truly displayed his own cleverness by enchanting the boulder. He caused it to roll away from Sisyphus before Sisphus reached the top of the hill, which ended up consigning Sisyphus to an eternity of useless efforts and unending frustration in rolling the boulder up the hill.

More Info: en.wikipedia.org