First, we have King Athamas, who grows tired of his first wife, Nephele. He decides to marry Princess Ino of Corinth, a woman who wants to get rid of Nephele's children, Phrixus and Helle, so that her own children will be the king's only heirs. Hermes sends a golden ram to save these children, though Helle falls into the sea and drowns on their way to Colchis.

Meanwhile, a man called Pelias steals the throne from his uncle, and that uncle's son and rightful heir, Jason, is secretly sent away for his own safety. Years later, Jason returns to demand his rightful position, and Pelias sends him to retrieve the Golden Fleece first. Pelias later dies when his daughters are tricked into killing him.

When Jason and the Argonauts reach Colchis, they meet King Aetes and his daughter, Medea, who ends up being a major help to Jason, saving his life more than once. Hera was looking out for Jason and had Cupid make Medea fall in love with him. These are all of the most significant characters in the text.