Jason of Pherae (Ancient Greek: Ἰάσων ὁ Φεραῖος) was the ruler of Thessaly during the period just before Philip II of Macedon came to power.
Controlling a highly trained mercenary force as well as the famous Thessalian cavalry, Jason briefly transformed Thessaly into a powerful Greek state and even spoke of invading the Persian Empire.
ὥσπερ ἔφη Ἰάσων ὁ Θετταλὸς δεῖν ἀδικεῖν ἔνια, ὅπως δύνηται καὶ δίκαια πολλὰ ποιεῖν (Ross, 1959).
The figure of Jason makes a sudden appearance in the history of classical Greece with Xenophon swiftly mentioning his name during his commentary on Theban hegemony during the 370s.
However, it has also been argued by Yalichev[5] that the Thessalian showed signs of pan-Hellenism in his approach to the prominent poleis of the south, an attitude exemplified particularly in his warning to Thebes not to destroy Sparta after the Battle of Leuctra.
Xenophon wrote of Jason: His generalship is of the highest quality—he is one who whether his methods are those of plain force, or working in the dark, or of seizing an unexpected advantage, very seldom fails to achieve his objects.