Prometheus (Forethought) was the son of the Titan Iapetus and was brother to the Titans Epimetheus (Afterthought) and Atlas. Prometheus and Epimetheus sided with Zeus and the other Olympians against the Titans and their brother and father because Prometheus could foresee the outcome of the conflict. Because of this, Prometheus and Epimetheus did not suffer the same fate as Iapetus and Atlas.
Prometheus was considered the father of mankind because he created them from clay. He only made men, no women, and let them loose to live in the world. The world was not a kind place though, it was filled with beasts and getting enough food to stay alive was a difficult task. This was not made any easier by Zeus, who insisted that mortal men sacrifice to the gods frequently and give the entire animal to the gods. Prometheus appealed to Zeus to allow the mortals to give only a portion of the animal to the gods and to keep the rest for themselves. Zeus agreed, but the two could not agree on which parts would be reserved for the gods. Prometheus knew that Zeus wanted all the good parts of the animal and came up with a plan to trick him. Prometheus took an animal and divided the choice cuts of the meat from the bones and other less savory tissues. On the pile of bones, he placed fat and a small portion of nice meat on top to disguise it, but on the pile of good meat he placed some lesser meat and gristle. He had Zeus choose from the two piles and Zeus chose the bones and fat. Zeus was very angry when he found out, and he never forgave Prometheus for tricking him.
Men now had meat, but they still had difficulty surviving because they could not keep warm or cook their food. Prometheus knew that fire would save them, but Zeus kept fire for the gods alone. So again, Prometheus thought up a plan. He took a red-hot coal and hid it inside a woody fennel stalk to give to mortals. Now the mortals could cook and keep warm and they were much happier; they worshipped Prometheus as the inventor of all the arts of civilization. But when Zeus saw mankind using fire, he became furious at having been tricked once again. He ordered that Prometheus be nailed to a lonely spot in the Caucasus Mountains. Every day an eagle would come every day to peck out his liver, but every night Prometheus’ liver would grow back so the eagle could eat it again. But Zeus was not finished with his punishments; now he wanted to punish mankind. Zeus then had Hephaestus build a beautiful woman, named Pandora (All Gifts), because each of the gods had given her a gift, and he sent her to Epimetheus. Even though Prometheus had warned his brother not to accept any gift from the gods, Epimetheus (true to his name) forgot all about his brother’s warning. As soon as Epimetheus saw Pandora, he knew he had to have her for his wife. But Pandora brought with her a jar (not a box) that was filled with evils. And once she opened her jar, all the evils flew out into the world; only hope stayed behind as a comfort for mankind.
Prometheus remained chained to the mountains until Heracles shot the eagle with his arrow and set the Titan free while on his labor to bring back the Apples of the Hesperides [see the 12 Labors of Heracles]. Zeus allowed Heracles to free Prometheus because he held some very useful knowledge that he would only divulge once he had been freed. After he was freed, Prometheus informed Zeus that the goddess Thetis, with whom Zeus was infatuated, was fated to give birth to a son who would be greater than his father [see Intro to Iliad]. Before Zeus knew this prophecy, he and Poseidon had been rivals for Thetis’ hand, but once the prophecy was known, neither god wanted anything to do with her. Zeus and Poseidon agreed that Thetis should be safely married off to a mortal. And that is how Thetis, a sea-goddess, came to marry Peleus, who was only a mortal. For the story of their wedding and the identity of the son (who did turn out to be greater than his father), see the Introduction to the Iliad.