Ptolemy I (367 - 283 BC reigned 305 - 283 BC), founder of the dynasty of the same name, son of Lagus, a Macedonian nobleman of Eordaea, was one of Alexander the Great's most trusted generals, and among the seven "body-guards" attached to his person.
He plays a principal part in the later campaigns of Alexander in Afghanistan and India. At the Susa marriage festival in 324 BC Alexander caused him to marry the Persian princess Artacama; but there is no further mention of this Asiatic bride in the history of Ptolemy.
When Alexander died in 323 BC the resettlement of the empire at Babylon is said to have been made at Ptolemy's instigation. At any rate he was now appointed satrap of Egypt under the nominal kings Philip Arrhidaeus and the young Alexander.
He at once took a high hand in the province by killing Cleomenes, the financial controller appointed by Alexander the Great; he also subjugated Cyrenaica. He contrived to get possession of Alexander's body which was to be interred with great pomp by the imperial government and placed it temporarily in Memphis. This act led to an open rupture between Ptolemy and the imperial regent Perdiccas. But Perdiccas perished in the attempt to invade Egypt (321 BC).
In the long wars between the different Macedonian chiefs which followed, Ptolemy's first object is to hold his position in Egypt securely, and secondly to possess the Cyrenaica, Cyprus and Palestine (Coele-Syria). His first occupation of Palestine was in 318 BC, and he established at the same time a protectorate over the petty kings of Cyprus. When Antigonus, master of Asia in 315 BC , showed dangerous ambitions, Ptolemy joined the coalition against him, and, on the outbreak of war, evacuated Palestine. In Cyprus he fought the partisans of Antigonus and re-conquered the island (313 BC). A revolt of Gyrene was crushed in the same year.
In 312 BC Ptolemy, with Seleucus, the fugitive satrap of Babylonia, invaded Palestine and beat Demetrius, the son of Antigonus, in the great battle of Gaza. Again he occupied Palestine, and again a few months later, after Demetrius had won a battle over his general and Antigonus entered Syria in force, he evacuated it. In 311 BC a peace was concluded between the combatants, soon after which the surviving king Alexander was murdered in Macedonia, leaving the satrap of Egypt absolutely his own master. The peace did not last long, and in 309 BC Ptolemy commanded a fleet in person which detached the coast towns of Lycia and Caria from Antigonus and crossed to Greece, where Ptolemy took possession of Corinth, Sicyon and Megara (308 BC). In 306 BC a great fleet under Demetrius attacked Cyprus, and Ptolemy's brother, Menelaus, was defeated and captured in the decisive battle of Salamis. The complete loss of Cyprus followed. Antigonus and Demetrius now assumed the title of kings; Ptolemy, as well as Cassander, Lysimachus and Seleucus I Nicator, answered this challenge by doing the same.
In the winter (306 BC) Antigonus tried to follow up the victory of Cyprus by invading Egypt, but here Ptolemy was strong, and held the frontier successfully against him. Ptolemy led no further expedition against Antigonus overseas. To the Rhodians, besieged by Demetrius (305 BC/304 BC), he sent such help as won him divine honours in Rhodes and the surname of Soter ("saviour"). When the coalition was renewed against Antigonus in 302 BC, Ptolemy joined it, and invaded Palestine a third time, whilst Antigonus was engaged with Lysimachus in Asia Minor. On a report that Antigonus had won a decisive victory, for a third time he evacuated the country. But when news came that Antigonus had been defeated and slain at Ipsus (301 BC) by Lysimachus and Seleucus, Ptolemy occupied Palestine for the fourth time.
The other members of the coalition had assigned Palestine to Seleucus after what they regarded as Ptolemy's desertion, and for the next hundred years the question of its ownership becomes the standing ground of enmity between the Seleucid and Ptolemaic dynasties. Henceforth, Ptolemy seems to have mingled as little as possible in the broils of Asia Minor and Greece; his possessions in Greece he did not retain, but Cyprus he re-conquered in 295 BC/294 BC.
Cyrene, after a series of rebellions, was finally subjugated about 300 BC and placed under his stepson Magas. In 285 BC he abdicated in favour of one of his younger sons by Berenice, who bore his father's name of Ptolemy; his eldest (legitimate) son, Ptolemy Ceraunus, whose mother, Eurydice, the daughter of Antipater, had been repudiated, fled to the court of Lysimachus.
Ptolemy I Soter died in 283 BC at the age of 84. Shrewd and cautious, he had a compact and well-ordered realm to show at the end of fifty years of wars. His name for bonhomie and liberality attached the floating soldier-class of Macedonians and Greeks to his service. Nor did he neglect conciliation of the natives. He was a ready patron of letters, and the great library, which was Alexandria's glory, owed to him its inception. He wrote himself a history of Alexander's campaigns, distinguished by its straightforward honesty and sobriety.