 He served as a general for Alexander Balas, during the civil war which the latter fought with Demetrius II Nicator.In 145 BC, when Alexander's father-in-law Ptolemy VI of Egypt switched his support to Demetrius II and invaded Syria, Diodotus and a man called Hierax were in command of the city of Antioch.They surrendered Antioch to Ptolemy and declared him king of the Seleucid Empire.