king of Egypt (285–246 BC), second king of the Ptolemaic dynasty, who extended his power by skillful diplomacy, developed agriculture and commerce, and made Alexandria a leading centre of the arts and sciences.

Reigning at first with his father, Ptolemy I Soter, he became sole ruler in 283–282 and purged his family of possible rivals. This dynastic strife led also to the banishment of his first wife, Arsinoe I, daughter of King Lysimachus of Thrace. Ptolemy then married his sister, Arsinoe II, an event that shocked Greek public opinion but was celebrated by the Alexandrian court poets. Taking advantage of the difficulties of the rival kingdoms of the Seleucids and Antigonids, Ptolemy II extended his rule in Syria, Asia Minor, and the Aegean at their expense and asserted at the same time his influence in Ethiopia and Arabia. Egyptian embassies to Rome as well as to India reflect the wide range of Ptolemy's political and commercial interests.

While a new war with the Seleucids (from 274 to 270) did not affect the basic position of the rival kingdoms, the so-called Chremonidean War (268?–261), stirred up by Ptolemy against Antigonus II Gonatas, king of Macedonia, resulted in the weakening of Ptolemaic influence in the Aegean and brought about near disaster to Ptolemy's allies Athens and Sparta. Ptolemy was no more successful in the Second Syrian War (Syrian Wars) (c. 260–253), fought against the coalition of the Seleucid king Antiochus II and Antigonus Gonatas. The unsuccessful course of the military operations was compensated for, to a certain degree, by the diplomatic skill of Ptolemy, who first managed to lure Antigonus into concluding a separate peace (255) and then brought the war with the Seleucid (Seleucid kingdom) Empire to an end by marrying his daughter, Berenice—provided with a huge dowry—to his foe Antiochus II (Antiochus II Theos). The magnitude of this political masterstroke can be gauged by the fact that Antiochus, before marrying the Ptolemaic princess, had to dismiss his former wife, Laodice. Thus freed for the moment from Seleucid opposition and sustained by the considerable financial means provided by the Egyptian economy, Ptolemy II devoted himself again to Greece and aroused new adversaries to Antigonid Macedonia. While the Macedonian forces were bogged down in Greece, Ptolemy reasserted his influence in the Aegean, making good the setback suffered during the Chremonidean War. He further improved his position by arranging for the marriage of his son (and later successor) Ptolemy III Euergetes to the daughter of King Magas of Cyrene, who had proved so far a very troublesome neighbour. Not aiming at outright hegemony (even less imperialistic conquest) in the Hellenistic (Hellenistic Age) world of the eastern Mediterranean, Ptolemy II tried nonetheless to secure for Egypt as good a position as possible, holding at large his rivals beyond a wide buffer zone of foreign possessions. Without being completely successful, he managed to let his allies bear the brunt of the heaviest reverses, healing his own military wounds with diplomatic remedies. The influence on Ptolemy of his wife and sister Arsinoe II, particularly in foreign affairs, was certainly substantial, though not as extensive as claimed by some contemporary authors.

Ptolemy II's record in domestic affairs is no less impressive. From pharaonic times onward, agriculture and the work of artisans in Egypt had been highly organized. Under Ptolemy's supervision and with the help of Greek administrators, this system developed into a kind of planned economy. The peasant masses of the Nile Valley provided cheap labour, so that the introduction of slavery on a broad basis was never considered an economic necessity in Ptolemaic Egypt. Ptolemy II became a master at the fiscal exploitation of the Egyptian countryside; the capital, Alexandria, served as the main trading and export centre. Ptolemy II displayed a vivid interest in Greek as well as in Egyptian religion, paid visits to the sanctuaries in the countryside, and spent large sums erecting temples. Anxious to secure a solid position for, and religious elevation of, his dynasty, the King insisted upon divine honours not only for his parents but also for his sister and wife Arsinoe II and himself as theoi adelphoi (“brother gods”). He thus became one of the most ardent promoters of the Hellenistic ruler cult, which in turn was to have a far-reaching influence on the cult of the Roman emperors.

Under Ptolemy II, Alexandria also played a leading role in arts and science. Throughout the whole Mediterranean world the King acquired a reputation for being a generous patron of poets and scholars. Surrounding himself with a host of court poets, such as Callimachus and Theocritus, he expanded the library and financed the museum (Alexandrian Museum), a research centre founded as a counterweight to the more antimonarchial Athenian schools. Learning there was not confined to philosophy and literature but extended also to include mathematics and natural sciences. The age of Ptolemy II coincided with the apex of Hellenistic civilization; its vigour and glamour were a result of the still fresh forces of Greek leadership in the eastern Mediterranean. Ptolemy II was no man of peace, but neither was he one of the warlike Hellenistic soldier-kings. A prudent and enlightened ruler, he found his strength in diplomatic ability and his satisfaction in a vast curiosity of mind.