king of the Seleucid dominions in the Middle East, who succeeded his father, Antiochus I, in 261 BC and spent much of his reign at war with Egypt, recovering much territory in Anatolia.

Finding a willing ally in Antigonus (Antigonus II Gonatas), ruler of Macedonia, who had suffered at the hands of Ptolemy II (Ptolemy II Philadelphus) of Egypt, Antiochus waged the Second Syrian War (259–255) against Ptolemy to avenge his father's losses. While Antigonus defeated the Egyptian fleet at sea, Antiochus reconquered much of Anatolia, including the cities of Miletus and Ephesus, and also the Phoenician coast.

In Miletus, Antiochus overthrew a tyrant after he recaptured the city, and the citizens worshiped him as a god in thanksgiving. He later organized an empire-wide cult, as suggested by his epithet, Theos (God). He also established the freedom of the other Ionian cities. Further, he continued his predecessors' policies of encouraging the foundation of cities in his realm.

For unknown reasons, around 253, Antiochus dismissed his first queen, Laodice, and married Ptolemy's daughter Berenice. At his death in 246, a civil war erupted between the two queens. He was succeeded by his son Seleucus II, while another son, Antiochus Hierax, established himself in western Anatolia.