Ptolemy I Soter (Greek: Πτολεμαίος Σωτήρ, Ptolemaios Soter, i.e. Ptolemy the Savior, 367 BC—283 BC) was a Macedonian general who became the ruler of Egypt (323 BC—283 BC) and founder of the Ptolemaic Dynasty. In 305 BC he took the title of Pharaoh.
He was the son of Arsinoe of Macedonia -- either by her husband Lagus, a Macedonian nobleman, or by her lover, Philip II of Macedon (which would make him the half-brother of Alexander the Great if true). Ptolemy was one of Alexander the Great's most trusted generals, and among the seven "body-guards" attached to his person. He was a few years older than Alexander, and his intimate friend since childhood. He may even have been in the group of noble teenagers tutored by Aristotle. He was with Alexander from his first campaigns, and played a principal part in the later campaigns in Afghanistan and India. At the Susa marriage festival in 324 BC, Alexander had him marry the Persian princess Atacama. Ptolemy also had a consort queen in Thaïs, the famous Athenian hetaera and one of Alexander's companions in his conquest of the ancient world. Thaïs became his queen in Egypt, and even after he divorced her, she reportedly remained his friend, and kept the title of queen while in Memphis.
Successor of Alexander
When Alexander died in 323, Ptolemy is said to have instigated the resettlement of the empire made at Babylon. He was now appointed satrap of Egypt, under the nominal kings Philip Arrhidaeus and the infant Alexander IV; the former satrap, the Greek Cleomenes, stayed on as his deputy. Ptolemy quickly moved, without authorization, to subjugate Cyrenaica.
By custom, kings in Macedonia asserted their right to the throne by burying their predecessor. Probably because he wanted to pre-empt Perdiccas, the imperial regent, from staking his claim in this way, Ptolemy took great pains in getting his hands on the body of Alexander the Great, placing it temporarily in Memphis. Ptolemy then openly joined the coalition against Perdiccas. Perdiccas appears to have suspected Ptolemy of aiming for the throne himself, and maybe decided that Ptolemy was his most dangerous rival. Ptolemy executed Cleomenes for spying on behalf of Perdiccas — this removed the chief check on his authority, and allowed Ptolemy to obtain the huge sum that Cleomenes had accumulated. 
In 321 BC, Perdiccas invaded Egypt. Ptolemy decided to defend the Nile, and Perdiccas's attempt to force it ended in fiasco, with the loss of 2000 men. This was a fatal blow to Perdiccas' reputation, and he was murdered in his tent by two of his subordinates. Ptolemy immediately crossed the Nile, to provide supplies to what had the day before been an enemy army. Ptolemy was offered the regency in place of Perdiccas; but he declined. Ptolemy was consistent in his policy of securing a power base, while never succumbing to the temptation of risking all to succeed Alexander.
In the long wars that followed between the different Diadochi, Ptolemy's first goal was to hold Egypt securely, and his second was to secure control in the outlying areas: Cyrenaica and Cyprus, as well as Syria, including the province of Judea. His first occupation of Syria was in 318 BC, and he established at the same time a protectorate over the petty kings of Cyprus. When Antigonus One-Eye, master of Asia in 315 BC, showed dangerous ambitions, Ptolemy joined the coalition against him, and on the outbreak of war, evacuated Syria. In Cyprus, he fought the partisans of Antigonus, and re-conquered the island (313 BC). A revolt in Cyrene was crushed the same year.
In 312 BC, Ptolemy and Seleucus, the fugitive satrap of Babylonia, both invaded Syria, and defeated Demetrius Poliorcetes ("sieger of cities"), the son of Antigonus, in the Battle of Gaza. Again he occupied Syria, and again—after only a few months, when 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 this, the surviving 13-year-old king, Alexander IV, was murdered in Macedonia, leaving the satrap of Egypt absolutely his own master. The peace did not last long, and in 309 BC Ptolemy personally commanded a fleet that detached the coastal towns of Lycia and Caria from Antigonus, then crossed into Greece, where he 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 another decisive Battle of Salamis. Ptolemy's complete loss of Cyprus followed.
The satraps Antigonus and Demetrius now each assumed the title of king; Ptolemy, as well as Cassander, Lysimachus and Seleucus I Nicator, responded by doing the same. In the winter of 306 BC, Antigonus tried to follow up his victory in Cyprus by invading Egypt; but Ptolemy was strongest there, and successfully held the frontier against him. Ptolemy led no further overseas expeditions against Antigonus. However, he did send great assistance to Rhodes when it was besieged by Demetrius (305 BC/304 BC),. Once rescued, the Rhodians instituted a festival to worship Ptolemy as Soter ("saviour").
When the coalition against Antigonus was renewed in 302 BC, Ptolemy joined it, and invaded Syria a third time, while Antigonus was engaged with Lysimachus in Asia Minor. On hearing a report that Antigonus had won a decisive victory there, he once again evacuated Syria. But when the news came that Antigonus had been defeated and slain by Lysimachus and Seleucus at the Battle of Ipsus in 301 BC, he occupied Syria a fourth time.
The other members of the coalition had assigned all Syria to Seleucus, after what they regarded as Ptolemy's desertion, and for the next hundred years, the question of the ownership of southern Syria (ie, Judea) produced recurring warfare between the Seleucid and Ptolemaic dynasties. Henceforth, Ptolemy seems to have mingled as little as possible in the rivalries between Asia Minor and Greece; he lost what he held in Greece, but reconquered Cyprus 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, Ptolemy abdicated in favour of one of his younger sons by Berenice -- Ptolemy II Philadelphus, who had been co-regent for three years. 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 forty years of war. His reputation for bonhomie and liberality attached the floating soldier-class of Macedonians and Greeks to his service, and was not insignificant; nor did he wholly neglect conciliation of the natives. He was a ready patron of letters, founding the Great Library of Alexandria. He himself wrote a history of Alexander's campaigns that has not survived. This used to be considered an objective work, distinguished by its straightforward honesty and sobriety. However, Ptolemy is considered to have exaggerated his own role, and to have had propagandist aims in writing his History. Although now lost, it was a principal source for the surviving account by Arrian of Nicomedia.
- Ptolemaic Dynasty - period of Egyptian history during the Ptolemaic dynasty.
- Ptolemy Soter I at LacusCurtius — (Chapter II of E. R Bevan's House of Ptolemy, 1923)
- Ptolemy I (at Egyptian Royal Genealogy, with genealogical table)
- Livius, Ptolemy I Soter by Jona Lendering
- A genealogical tree of Ptolemy, though not necessarily reliable
- Ptolemy I Soter’s self-promotion in his history of Alexander the Great