The younger son of Antiochus II & his sister Laodice whose ambitions brought the Seleucid dynasty close to extinction.  His brother, Seleucus II, made him governor of Asia Minor during his war with Egypt (246-241 BCE).  But instead of helping him, Hierax was encouraged by his mother to use his brother's misfortunes to seize the Seleucid throne for himself. With the aid of the Celts of Galatia he defeated his brother at Ancyra (236 BCE) but was himself driven into exile by the ruler of Pergamum (227 BCE).  He escaped the following year only to be killed by his former allies, the Galatians.

References: Justin, Epitome 27.2-3

Other resources on line:

• Antiochus Hierax - brief entry in Wikipedia's web.

• Justinus: Epitome of Pompeius Trogus' "Philippic histories" 25-30 - J. S. Watson's 1853 translation of a third c. Latin paraphrase of a 1st c. historian's account of the political chaos surrounding the Gallic invasion of the Balkans and Asia Minor.

This silver tetradrachma minted by Hierax mimics his father's coinage.  The face bears the king's image wearing the royal diadem.  The other side portrays Apollo with bow & arrow seated on a phallic stone.  The Greek inscription reads from right to left, Basileos Antiochou ("of King Antiochos").