Prometheus is the god protector of mankind. This is the whole legend of Prometheus:
One day, a quarrel broke because of a bull: no one agrees on the pieces that will be given to the gods and those that will be given to mankind. Prometheus was chosen to be the arbiter of the conflict. Prometheus makes two bags. In the first, there is all the flesh, but he hides it behind the stomach, which is the least delicious part of the animal. In the second, there are bones hidden under a layer of creamy white fat (Gods love to eat fat). Zeus chose the second bag. (That's why the ancient Greeks sacrificed only the fat and the bones of an animal).
When Zeus discovers the ruse, he punishes Prometheus by removing fire from mankind. Prometheus visits Athena to ask her to help him enter Olympus without being seen. She helps him. He steals fire from the gods and give it to mankind.
Zeus decides to avenge himself upon mankind. He asks Hephaestus to make a woman with clay and give her life. This woman is Pandora, the first woman. Zeus gives her a jar, in modern times referred to as a box, or casket, containing all the evils which can possibly beset mankind, and sends her to Epimetheus, the brother of Prometheus, and who - despite Prometheus' warning not to accept any gifts from the gods, takes her in. Out of curiosity, Pandora opens the jar and allows all the ills of mankind to escape into the world. Horrified, she frantically shuts the jar, but all the evils had escaped, leaving only Hope. Hope, of course, makes bearable all evils, so while mankind now has woman and, with her, all the bad things, humans also have Hope, so things aren't as terrible as they seem at first.
Increasingly irritated, Zeus orders to enchain Prometheus in the Caucasus Mountains, where a vulture will eat his self-regenerating liver all day, every day, for eternity. Later, Zeus is sorry for having inflicted this punishment on Prometheus because he once gave him a good advice: to not marry Thetis, in order to avoid having a child that would be more powerful than Zeus and grow up to dethrone him.
Zeus finally orders Heracles, or Hercules to the Romans, to release Prometheus. Since he condemned Prometheus to eternal punishment, Zeus saves face by telling Prometheus that, to give the impression of being still a prisoner, he must wear a ring made of metal chains. In other versions, Heracles slays the eagle and breaks Prometheus' chains, without instructions from Zeus.
There's little information on how Prometheus fared on gaining his freedom, but given Zeus' reputation, the Titan probably kept his head down and is still, somewhere, leading a very quiet and blameless life.