Demetrius II Aetolicus (Greek: Δημήτριος Αιτωλικός) son of Antigonus Gonatas, reigned as king of Macedonia from the winter of 239 to 229 BC. He belonged to the Antigonid dynasty and was born in 275 BC. There is a possibility that his father had already elevated to him to position of power equal to his own before his death. If this had occurred it would be dated at 256 or 257 BC.
He had already during his father's lifetime distinguished himself by defeating Alexander II of Epirus at Derdia and so saving Macedonia (circa 260 BC). On his accession he had to face a coalition which the two great leagues, usually rivals, the Aetolian and Achaean, formed against the Macedonian power. He succeeded in dealing this coalition severe blows, wresting Boeotia from their alliance. The revolution in Epirus, which substituted a republican league for the monarchy, gravely weakened his position.
During his reign his kingdom extended to Euboea, Magnesia, Thessaly and its environs, excluding Dolopia and possibly Peparethos and Phthiotic Achaia.
At 236 BC he invaded Boetia, making the Boetians submit immediately.
In 234 BC due to the Federal Republic replacing monarchy in Epirus led to the events of 231 BC, Demetrius hired Agron for military aid against advancing Aetolians. His kingdom was not threatened by the Illyrian Ardiaei ruled by Agron despite them having gathered the greatest force in their history (around 231 BC), but Epirus needed some sort of force to deter them.
Demetrius in the end of his reign defended his domain from the tribal peoples of the north. A battle with the Dardanians turned out disastrously, and he died shortly afterwards, leaving Philip, his son by Chryseis, still a child.
Former wives of Demetrius were Stratonice of Macedon, the daughter of the Seleucid king Antiochus I, Phthia (239 BC) the daughter of Alexander of Epirus, and Nicaea, the widow of his cousin Alexander. The chronology of these marriages is a matter of dispute. From his marriage to Stratonice, he had a daughter called Apama III .
Information regarding the life of Demetrius are drawn mainly from inscription as only Plutarch writes of him, in Life of Aratus, and Polybius makes scarce mentions of him.
Son of Philip III., of Macedonia, an excellent prince, greatly beloved by his countrymen, and sent by his father as a hostage to Rome, where he also made many friends. He was subsequently liberated, and not long after paid a second visit to the capital of Italy as an ambassador from Philip, on which occasion he obtained favourable terms for his father, when the latter was complained of to the Roman Senate by the cities of Greece. Returning home loaded with marks of distinction from the Romans, and honoured by the Macedonians themselves, who regarded him as the liberator of their country, he excited the jealousy of his own father and the envy and hatred of his brother Perses. The latter eventually accused him of aspiring to the crown, and of carrying on, for this purpose, a secret correspondence with the Romans. Philip, lending too credulous an ear to the charge, put his son Demetrius to death, and only discovered when too late the utter falsity of the accusation (Liv.xxxiii. 30; xxxix. 35 foll.; xl. 5, 24Liv., 54 foll.).