This guy is known for being a total smarty-pants. He's also known for being totally evil. Whether it's seducing his niece in a plot to kill his brother or killing innocent guests in his home, Sisyphus is always up to no good. His most famous feats of cleverness came when he tricked his way out of the Underworld twice in a row, by first fooling Thanatos, god of death, and then Persephone, queen of the Underworld.
While Sisyphus's clever feats are pretty impressive, he gets his in the end. After Hermes drags the crafty mortal down to the Underworld for the last time, Zeus makes an example of Sisyphus by dooming him to roll a giant boulder up a hill for all eternity. It's kind of ironic that a guy who was famous for his brains is forced to do physical labor for all eternity, right? In the end, Sisyphus becomes a warning for other mortals to not let hubris (pride) ever convince them that they are truly cleverer than the gods.