Short answers, pulled from the story.
Sisyphus was the founder and first king of Ephyra, the city now known as Corinth. He was the son of King Aeolus of Aeolia and was known from Homer onward as the craftiest of men. His punishment in the underworld, rolling a boulder up a hill for eternity, made his name a byword for endless, futile labor.
Sisyphus was condemned to push an immense boulder up a hill in Tartarus as punishment for repeatedly cheating death and for his hubris in believing his cleverness surpassed that of Zeus. His crimes included revealing Zeus's abduction of Aegina, trapping Thanatos so no one could die, and tricking Persephone into letting him return to the living world.
Sisyphus cheated death twice. First, he captured and chained Thanatos, the god of death, preventing anyone on Earth from dying until Ares intervened. Second, he instructed his wife not to bury him, then used the excuse of her "disrespect" to persuade Persephone to release him back to the world of the living, where he refused to return to the underworld for years.
In his 1942 essay The Myth of Sisyphus, Albert Camus interpreted Sisyphus as a symbol of the absurdity of human life. Camus concluded that one must imagine Sisyphus happy, arguing that the struggle itself toward the heights is enough to fill a man's heart.
Sisyphean describes tasks that are laborious, futile, and never-ending, drawn from the punishment inflicted on Sisyphus. The adjective entered the language through classical influence on contemporary culture and is still used today.
In some versions of the myth, Sisyphus was the true father of Odysseus by Anticleia, rather than Laertes. Both Sophocles in Philoctetes and Euripides in Cyclops referenced this alternative parentage, though the mainstream tradition given in the Odyssey names Laertes as Odysseus's father.