Achaeus (Ancient Greek: Ἀχαιός, Akhaios; died 213 BC) 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 Callinicus, the father of Antiochus III the Great He accompanied Seleucus Ceraunus, the son of Callinicus, in his expedition across mount Taurus against Attalus I, and after the assassination of Seleucus Ceraunus revenged his death; and though he might easily have assumed the royal power, he remained faithful to the family of Seleucus.