Once upon a time, in a not-so-nice part of Greece (back in the time of Mythology), there lived a king named Sisyphus. By the sound of his name you might think that he was bullied a lot. You would be wrong because he was meaner, nastier, and more powerful than anyone else. Also he was king and had a lot of soldiers at his command.
Sisyphus had lots of bad habits like chewing with his mouth open and killing travelers and guests. (Killing guests back then was an especially Wrong Thing To Do.) But Sisyphus had a marvelous time being a despot and decided that Manners weren’t going to intrude on his tyranny.
For reasons that are complicated and not all that interesting, Zeus got good and mad at Sis. Zeus ordered Thanatos to chain up Sisyphus in the lowest level of Hades.
On the one hand, Thanatos was a minor figure in Greek mythology. On the other hand, he was Death, so chaining people in Hades was well within his job description.
Sisy didn’t really like the idea of being chained up, so he tricked Thanatos by asking Thanatos (who after all wasn’t the god of wisdom) to demonstrate how the chains worked. Flattered, Thanatos obliged and Sisyphus trapped Thanatos in the aforementioned chains.
Back in the rest of the world, while Thanatos was chained up no one could die. For a short time, this wasn’t a big deal, but people were pretty accustomed to Death, especially the warriors who liked to see people die (because that was the whole point of fighting). Ares (our favorite god of war) was particularly put out, so he freed Thanatos and turned Sisyphus over to him.
Because of his trickery in this and other things and his hubris in thinking he was more clever than Zeus (have we not been clear that it is never wise to think you’re smarter/prettier/stronger than one of the gods), King Sisyphus was punished. And the Greek gods were known for their ability to punish people.
Sisyphus was made to push an enormous boulder up an even more enormous hill. Only just before he got to the top, the enchanted boulder would roll away from him and to the bottom of the hill. Rinse and repeat for all eternity.