Prometheus, as a result of the fact that he stood up to Zeus, became a symbol of the individual who takes a stand against unjust authority: a Romantic ideal. His championing of humanity, and his willingness to help us despite incurring Zeus's anger and resentment, also enhances this symbolism. Prometheus was considered, by many, to be the "savior of humankind." First, he tricked Zeus by killing an animal and making two piles: he covered gristle and bone with a thin layer of appealing meat and covered most of the good meat and fat with a few bones and other inedible parts. He then gave Zeus his choice of which pile should be his when humans provide him offerings; Zeus, based on appearances, chooses the pile of mostly inedible materials because it looked appealing, and he is angry when he realizes that Prometheus tricked him.
Further, when his brother, Epimetheus, gave animals all the sharp teeth, tough hides, and powerful claws, Prometheus gave us something even better: fire. He took it from the sun itself so that we could keep warm without hides and cook our food so that we will not need sharp teeth or claws. Then, when Zeus heard a prophecy that he would father a son who would grow up to overthrow him, he approached Prometheus to find out the name of the child's mother. Prometheus, however, would not tell him, and so Zeus chained him to a mountain and sent a huge eagle to tear out his liver every day. Prometheus never did give in, but Zeus eventually backed down.
Finally, Prometheus also saved the human race when Zeus sent a giant flood to cover the earth and wipe out a corrupt humanity. Prometheus told a young couple (his son and niece) to build a wooden ark so that they could survive the flood. They did so, and when the waters receded, they were so pious that Zeus allowed them to live. When they cast stones behind them, the stones sprang up into people and these stone-people became the next race of humans.
Prometheus's history of standing up to Zeus, a Zeus who demands the best meat, who demands information, who would withhold the means for humans to stay alive, who would flood the earth and wipe out humanity, makes him a true hero to humans. This notion of a single individual who possesses such power as a result of his own bravery and genius and goodness became important to the Romantics because they thought so highly of the individual's potential and ability.