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The longer version is that Sisyphus as a King was very smart, manipulative and confident (he was also kind of cruel) but he was a strong king.
Zeus kidnapped Aegina (a nymp) and her father went to ask Sisyphus for help to get her back in exchange for a river.
When Zeus heard this he got angry and asked Death to get Sisyphus. And that's where the story I told before begins :)
So Sisyphus myth goes like this:
When Death came to fetch him, Sisyphus chained Death up so that no one could die. Finally, Ares came to aid Death, and Sisyphus had to submit. In the meantime, Sisyphus had told his wife, Merope, not to perform the usual sacrifices and to leave his body unburied. Thus, when he reached the underworld, he was permitted to return to punish her for the omission. Once back at home, Sisyphus continued to live to a ripe old age before dying a second time.
The gods didn't like this, so as punishment he was told he had to push a rock to the top of a mountain, but once he is almost at the top, the rock falls down again and basically all his work meant nothing, so he goes down to do the same thing over and over again. A meaningless life basically.
The funny thing about this myth is that nobody really forces him to do so, there is nothing pushing him to keep on doing this, he just does it because he's stubborn and wants to win against the gods.