Antigonus was a son of Greek Macedonian prince Demetrius the Fair from his first marriage to Greek noblewoman Olympias of Larissa. His brother is a little known Greek Macedonian nobleman called Echecrates and Antigonus’ paternal uncle was the Greek Macedonian king Antigonus II Gonatas. On the death of King Demetrius II of Macedon (229 BC), Antigonus became guardian of Demetrius II's son, Philip. In 227 BC Antigonus married widow of Demetrius II, Phthia, deposing the young Philip, and became king.
