He is the symbol of intelligence and sacrifice. While making the humans, there was an error due to his brother. So, in order to save the humans, he brought fire to them from Mount Olympus (symbolical for intelligence) to help them prevail. This anger Zeus, who in turn punished him. Prometheus is now chained to a rock, where each day a falcon or other bird of prey (I forgot) comes to eat his liver. It then regenerates over night to repeat the process for all eternity. I think he's eventually freed by Hercules though. I assume he's basically invincible, due to the fact that he never dies during this process.