Prometheus was a god from the old order, the Titans, who had now all been overthrown by a group of young upstarts, the Olympians (all except for Prometheus, that is). Rather than go down in honor, this half-god Prometheus, in order to avoid further violence, chose to desert the Olympian forces. In fact, he was instrumental in Zeus' usurpation of the throne from the old Titan king Chronus. In the new order, Zeus stood as chief god.
Now one of Zeus' first objectives was to destroy the rice of men, who, until then, had been a primitive, unenlightened and miserable lot. Zeus' intent was to replace mankind with a new, more noble race, servile to the gods' every whim.
When the destructive proclamation went out, however, Prometheus alone objected to Zeus' heartless proposal. He saw in man a spark of divine promise that even the gods might envy, and in order to save the human race, he willingly and courageously committed a crime: he brought fire down from heaven and taught the mortals how to use it. Furthermore, he tutored them in practical arts, applied sciences and philosophy, so that he might edify, ennoble and empower them.
But these saving acts were deemed highly treasonous; such knowledge in the hands of mortals threatened to put them on an equal footing with the gods themselves. Furious, Zeus commanded the Olympian blacksmith god of fire, Hephaestus, and the gods of Might and Force, Kratos and Bia, to seize Prometheus and shackle him to a barren mountainside. But Hephaestus approached his task halfheartedly. He had been taught to respect deity and he sympathized with