Seleucus II Callinicus in Wikipedia
Seleucus II Callinicus or Pogon (Greek: Σέλευκος Β' Καλλίνικος , the epithets meaning "beautiful victor" and "bearded", respectively), was a ruler of the Hellenistic Seleucid Empire, who reigned from 246 to 225 BC. After the death of this father, Antiochus, he was proclaimed king by his mother, Laodice in Ephesos, while her partisans at Antioch murdered Berenice and her son, another Antiochus.
This dynastic feud began the Third Syrian War. Ptolemy III, who was Berenice's brother and the ruler of Egypt, invaded the Seleucid Empire and marched victoriously to the Tigris or beyond. He received the submission of the Seleucid Empire's eastern provinces, while Egyptian fleets swept the coast of Asia Minor.
Seleucus managed to maintain himself in the interior of Asia Minor. When Ptolemy returned to Egypt, Seleucus recovered Northern Syria and the nearer provinces of Iran. However, Antiochus Hierax, a younger brother of Seleucus, was set up as a rival in Asia Minor against Seleucus by a party to which Laodice herself adhered.
At Ancyra (about 235 BC) Seleucus sustained a crushing defeat and left the country beyond the Taurus to his brother and the other powers of the peninsula. Seleucus then undertook an anabasis to regain Parthia, the results of which came to nothing. According to some sources, he was even taken prisoner for several years by the Parthian king. Other sources mention that he established a peace with Arsaces I, who recognized his sovereignty.
In Asia Minor, Pergamon now rose to greatness under Attalus I. Antiochus Hierax, after a failed attempt to seize his brother's dominions when his own were vanishing, perished as a fugitive in Thrace in 228 or 227 BC.
About a year later, Seleucus was killed by a fall from his horse. Seleucus II married his cousin Laodice II, by whom he had five children and among them were: Antiochis, Seleucus III Ceraunus and Antiochus III the Great. He was succeeded by his elder son, Seleucus III Ceraunus, and later by his younger son Antiochus III the Great.
Seleucus in Harpers Dictionary of Classical Antiquities (1898)
Surnamed Callinīcus (246-226), the eldest son of Antiochus II. by his first wife Laodicé. The first measure of his administration, or rather that of his mother, was to put to death his stepmother Berenicé, together with her infant son. This act of cruelty produced the most disastrous effects. In order to avenge his sister, Ptolemy Euergetes, king of Egypt, invaded the dominions of Seleucus, and not only made himself master of Antioch and the whole of Syria, but carried his arms unopposed beyond the Euphrates and the Tigris. During these operations Seleucus kept wholly aloof; but when Ptolemy had been recalled to his own dominions by domestic disturbances, he recovered possession of the greater part of the provinces which he had lost. Soon afterward Seleucus became involved in a dangerous war with his brother Antiochus Hierax, who attempted to obtain Asia Minor as an independent kingdom for himself. This war lasted several years, but was at length terminated by the decisive defeat of Antiochus, who was obliged to abandon Asia Minor and take refuge in Egypt. Seleucus undertook an expedition to the East, with the view of reducing the revolted provinces of Parthia and Bactria, which had availed themselves of the disordered state of the Syrian Empire to throw off its yoke. He was, however, defeated by Arsaces, king of Parthia, in a great battle, which was long after celebrated by the Parthians as the foundation of their independence. After the expulsion of Antiochus, Attalus, king of Pergamus, extended his dominions over the greater part of Asia Minor; and Seleucus appears to have been engaged in an expedition for the recovery of these provinces, when he was accidentally killed by a fall from his horse, in the twenty-first year of his reign, 226. He left two sons, who successively ascended the throne, Seleucus Ceraunus and Antiochus, afterward surnamed the Great. His own surname of Callinicus was probably assumed after his recovery of the provinces that had been overrun by Ptolemy.