Prometheus is a Titan – a giant-like deity from Greek mythology originating in the 8th-century BC Greek poem Theogony. He is the son of Lapetos and the Oceanid Klymenê.
He was tasked by Zeus with creating human beings, and to shape them in the likeness of the gods. However, Zeus made one exception: human beings were not to have fire, and so he hid it from them. Knowing what an intelligent being could do with fire, Zeus was afraid that humanity might use it to overthrow the gods.
Prometheus duly created human beings, but was so taken with his creation that he decided to disobey Zeus. He stole fire from heaven and gave it to humanity, hidden inside a hollow fennel stalk. This of course gave them just that mastery of the world that Zeus had feared, and gods were indeed overthrown in the most radical sense possible: we stopped believing that they even exist.
Zeus was enraged at Prometheus’ disobedience, and determined to punish him in the most horrible way imaginable. So he nailed him to a mountain in the remote Caucasus mountains and sent an eagle to visit him every day. The eagle would tear out Prometheus’ liver, and then fly away. The liver would grow back over night, and the eagle would return the next day and tear it out all over again. And so on. Forever.
Or not quite forever. Many years later Hercules came by on one of his Labours, released Prometheus and shot the eagle in exchange for information. Prometheus was released, Zeus relented, and then… Who knows?
Sources of the myth
As is the case with many myths, and especially one so old, different scholars, playwrights, poets and so forth have added to the myth, embellished some points and refuted others. Some say Prometheus was tasked by Zeus with creating human beings, and to shape them in the likeness of the gods. A more common variant like that in the book Prometheus Bound, is that he was the champion of humanity, and gave us every skill, but did not create us. According to the Greek scholar Apollodorus, Prometheus completed his task by shaping humans from earth and water. Others say that he shaped us from clay.
You can purchase the excellent tragedy about our unfortunate Titan, Prometheus Bound, from Amazon. This was supposedly written by Aeschylus (an ancient Greek tragedian / playwright) circa 450BC.