Ptolemy I Soter I (i.e.

Ptolemy the Savior), also known as Ptolemy Lagides, c. 367 BCE – c. 283 BCE, is a Macedonian general under Alexander the Great, who became ruler of Egypt (323 BCE – 283 BCE) and founder of both the Ptolemaic Kingdom and the Ptolemaic Dynasty.

In 305/4 BCE, he takes the title of pharaoh.

His mother is Arsinoe of Macedon, and, while his father is unknown, ancient sources variously describe him either as the son of Lagus, a Macedonian nobleman, or as an illegitimate son of Philip II of Macedon (which, if true would have made Ptolemy the half-brother of Alexander).

Ptolemy is one of Alexander's most trusted generals, and is among the seven somatophylakes (bodyguards) attached to his person.

He is a few years older than Alexander, and has been his intimate friend since childhood.

Ptolemy serves with Alexander from his first campaigns, and plays a principal part in the later campaigns in Afghanistan and India.

At the Susa marriage festival in 324, Alexander has Ptolemy marry the Persian princess Artakama.

Ptolemy also has a consort in Thaïs, the Athenian hetaera and one of Alexander's companions in his conquest of the ancient world.