Antigonus III (Antigonus Doson) (ăntig´ənəs dō´sŏn,–sən), d. 221 BC, king of Macedon. On the death of Demetrius II he became regent for Demetrius' son Philip (Philip V). He married the widow of Demetrius, and in 227 he proclaimed himself king. The attacks of Cleomenes III on the Achaean League caused its leader, Aratus, to request help from Antigonus, who led his troops south in 224. In 222, Antigonus crushed Cleomenes at Sellasia in Laconea and took Corinth as his reward. Meanwhile he had reconstituted the Hellenic League, and when he died he left power in Greece as well as Macedon to Philip.