Antigonus III Doson was a half-cousin of his predecessor, Demetrius II Aetolicus. Doson's father was Demetrius the Fair (briefly king of Cyrene), the son of Demetrius Poliorcetes and his third wife, Ptolemaïs, daughter of Ptolemy I Soter and Eurydice, daughter of Antipater. As such, Demetrius the Fair was, on his father's side, a younger half-brother of Demetrius II's father, Antigonus II Gonatas, the son of Poliorcetes by his first wife, Phila, another of Antipater's daughters; as well as a nephew of both Ptolemy Keraunos and Meleager on his mother's side. According to Eusebius, Doson's own mother was a Thessalian noblewoman, Olympias, daughter of Pauliclitus of Larissa. Antigonus also had a brother named Echecrates, whose son, named Antigonus after Doson himself, was put to death by Perseus on the latter's accession to the throne of Macedon.