In Greek mythology, Prometheus the Titan was the son of Iapetus and Clymene. Among his brothers there were the titan Atlas and Epimetheus.
This means he was the cousin of Zeus. When the latter rose against his father, Cronus, and wanted to become the supreme ruler of the gods, Iapetus and the other Titans sided with Cronus, but Prometheus the Titan and his brother Epimetheus took Zeus's side (they knew from the goddess Themis, who had the gift of foretelling, that the brute force represented by the Titans will be defeated).
In some legends in Greek mythology, Prometheus made the man from clay, in a godlike shape. In other myths, however, he is not the maker of man, but just the benefactor of mankind.
According to some, Prometheus (the "forethought") and his brother Epimetheus (the "afterthought") had to give different abilities to the animals and to man. Epimetheus gave animals all kind of abilities (to run, to fly, to hide underground) and weapons (claws, fangs) until there was nothing left for the man. When Prometheus the Titan saw that, he decided to give man something different in order to be able to survive. So he took the arts from Athena and the fire from Hephaistos (or from the Sun's chariot) and gave them to man, and that's how man could defend himself from other animals and survive.
The first time an ox was sacrificed to the gods, Prometheus the Titan made two heaps: in one of them he put the bones, covered by the white fat, so it looked quite appetizing. In the other heap, he put the meat, covered by the entrails. Then Zeus had to choose what he liked best. The ruler of all gods (not too clever, after all), chose the heap covered by fat, thinking that the meat should be there too. That's why, ever since, when sacrificing to the gods, men kept the meat for themselves and burnt on the altar the fat and the bones, for the gods. (Well, I think people invented this legend as an excuse to why they kept the best part when sacrificing an animal - after all, why give the goodies to creatures they didn't even see?). Of course, Zeus was not happy with the deal, but he had to abide by it.
There is another version of the Prometheus myth of the fire: Because of the outcome of the deal with the sacrifice, Zeus decided to punish mankind and took fire away from them. Prometheus couldn't stand such an injustice, so he stole the fire from the gods and brought it back on Earth, in a hollow reed (or in a fennel stalk).
Of course Zeus was mad about it, so this time he thought of an even bigger punishment. For the mortals, he made a special creature - the woman. The first woman was called Pandora ("all gifts") and she was sent as a gift from the gods (she carried the well-known Pandora's box). Prometheus the Titan refused her, but his brother Epimetheus wouldn't listen to his advice and was just too happy to marry her. Anyway, the trick was that through Pandora, all evils came into the world (who created this legend surely "loved" women!).
The punishment for Prometheus the Titan was to be chained on Mount Caucasus forever. There, a vulture would come every day and devour his liver. At night, the liver would grow again, so as the next day the torture would begin anew. For thousands of years remained Prometheus bound on Mount Caucasus.
In Aeschylus's play Prometheus Bound, there appears Io, who had been transformed into a cow by Zeus in order to help her escape the jealousy of Hera (some help, I'd say). When their affair was discovered, Hera sent her a stinging insect to torment her, that's why she wandered everywhere and arrived where Prometheus the Titan was. She asked him about her future and he helped her, as he knew that later, one of Io's great-great-grandsons, Hercules, will rescue him. After 30.000 years, when Hercules came to Mount Caucasus, he killed the vulture with an arrow and freed Prometheus. Zeus let this happen as it would have brought greater glory to his beloved son. But, as he had sworn that Prometheus the Titan would remain forever chained to the rock, he had to wear a ring made of the iron of his chains, and with a piece of the rock he was tied to. And that's how the ring with a stone came into being!