By most accounts, Sisyphus was a bit of an arrogant, cocky individual. The founder and king of what became Corinth, in Greece, he seems to have made it his business to annoy and antagonise everyone around him, from mortals to gods. Unfortunately, like all egotistical people who aren’t as smart as they think they are, he overreached, and on betraying one of Zeus’s secrets, the god ordered Hades (or Thanatos, depending on the version) to chain up Sisyphus in Tartarus.
He tricked his captor, restraining Hades using the chains meant for him, resulting in nobody on Earth dying. Furious, the gods punished him, and Sisyphus ended up in the underworld. Hades made Sisyphus push a boulder up a steep hill in Tartarus, but, still angry from the betrayal, Zeus enchanted the boulder to roll away down to the bottom of the hill when it got close to the top. Sisyphus was then cursed to continually push this boulder up the hill for eternity.