Achaeus

Achaeus was a general and later a separatist ruler of part of the Greek Seleucid kingdom. He was the son of Andromachus, whose sister Laodice II married Seleucus II Callinicus, the father of Antiochus III the Great. He accompanied Seleucus III Ceraunus, the son of Callinicus, in his expedition across mount Taurus against Attalus I, and after the assassination of Seleucus III Ceraunus revenged his death; and though he might easily have assumed the royal power right then, he remained faithful to Antiochus III, brother of Seleucus III, for the time being, that is until he proclaimed himself king in 220 BC.