Jason was son of Æson, king of Thessaly, and Alcimĕde. He was an infant when Pelias, his uncle, who was left his guardian, sought to destroy him; but being, to avoid the danger, conveyed by his relations to a cave, he was there instructed by Chiron in the art of physic; whence he took the name of Jason, or the healer, his former name being Diomēdes. Arriving at years of maturity, he returned to his uncle, who, probably with no favorable intention to Jason, inspired him with the notion of the Colchian expedition and agreeably flattered his ambition with the hopes of acquiring the golden fleece.
Jason having resolved on the voyage, built a vessel at Iolchos in Thessaly, for the expedition, under the inspection, of Argos, a famous workman, which, from him, was called Argo: it was said to have been executed by the advice of Pallas, who pointed out a tree in the Dodonæan forest for a mast, which was vocal, and had the gift of prophecy.
The fame of the vessel, the largest that had ever been heard of, but particularly the design itself, soon induced the bravest and most distinguished youths of Greece to become adventurers in it, and brought together about fifty of the most accomplished young persons of the age to accompany Jason in this expedition; authors, however, are not agreed on the precise names or numbers of the Argonauts; some state them to have been forty-nine; others more, and amongst them several were of divine origin.
On his arrival at Colchis he repaired to the court of Æētes, from whom he demanded the golden fleece. The monarch acceded to his request, provided he could overcome the difficulties which lay in his way, and which appeared not easily surmountable; these were bulls with brazen feet, whose nostrils breathed fire, and a dragon which guarded the fleece. The teeth of the latter, when killed, Jason was enjoined to sow, and, after they had sprung up into armed men, to destroy them.
Though success attended the enterprise, it was less owing to valor, than to the assistance of Medēa, daughter of Æētes, who, by her enchantments, laid asleep the dragon, taught Jason to subdue the bulls, and when he had obtained the prize, accompanied him in the night time, unknown to her brother.
The return of the Argonauts is variously related; some contend it was by the track in which they came, and say that the brother of Medēa pursued them as far as the Adriatic, and was overcome by Jason; which occasioned the story that his sister had cut him in pieces, and strewed his limbs in the way, that her father, from solicitude to collect them, might be delayed in the pursuit.