Once upon a time there was a king called Aeson. He reigned until his brother Pelias dethroned him and took the power over Thessaly. Aeson died far from his country but he had a son who, like many other heroes, was brought up by the Centaur Chiron. This boy was Jason, and when he was old enough he left to Thessaly to claim his legitimate throne.
But Pelias was an intelligent king and he accepted the claim under just one simple condition. Jason should bring him the Golden Fleece of the king Aeetes from Kolchis, since he was too old to do it by himself. Of course, what he was really expecting was that Jason would die on the way, but the boy was too naive and he agreed.
The Golden Fleece
The Golden Fleece comes out of one of the rams from Hermes, which had golden fleece and could fly. Once, there was a king in Boeotia who dishonored his wife Nephele by marrying another woman. This hurt her and her children too much, so Nephele decided to send her children Phrixos and Helle far away. Then she got this ram from Hermes, put the kids on its back, and asked the ram to take them far away to the coast of the Black Sea. However, on the way Helle began to waver, fell down to the sea and died -giving with this name to the Hellespont.
Her brother Phrixos arrived safe to Kolchis, on the west coast of the Black Sea. There the king Aeetes kindly received him and the boy ended up marrying one of his daughters. Phrixos sacrificed the ram in honor to Zeus and made the fleece be nailed in a tree. The fleece was also guarded by a dragon, since the king got told by the oracle that he would live as long as this fleece stayed in his power.