The Golden Fleece

Once upon a time a man grew bored of his wife. He put her away and got himself another one. The mother was worried about the children, and Mercury offered her a golden ram that would take them to safety. This was done, and the ram was sacrificed.

Years later, an uncle didn't want his nephew, Jason, to become king. He told him that if he managed to bring back to fleece of the golden ram. The nephew agreed, and attempted the first maritime expedition. Fifty young men joined in, including Hercules, Theseus, Orpheus, and Nestor.

So Jason was confronted with a bunch of impossible tasks, but with the help of the sorceress Medea, he manages all of the them, marries Medea, goes home, and lives happily ever after.

This was, supposedly, really the first maritime expedition in Greece. Jason was probably a pirate, which is confirmed by the fact he brought back gold at the end. Maybe it's true, even though that would put all those heroes in a much less noble light.