Greek mythology is derived primarily from Greek literature and representations on visual media dating from the Geometric period (c. 900-800 BC) onward.
Ancient Greek mythology claimed that Zeus, as he had previously overthrown his father, Cronus, would in turn also be overthrown by a son. This story can be seen as the equivalent to the end of the world, or the end of an age. Prometheus revealed to him that this son would be born from Zeus and Thetis, if they copulated. In order to prevent this from happening, Zeus married Thetis to Peleus, a mortal hero. This union produced Achilles, the protagonist of the Iliad and one of the greatest heroes of Greek myth.