Argead dynasty
A Macedonian, Ptolemy was born in 367 BC. Ptolemy's mother was Arsinoe. According to Satyrus the Peripatetic, Arsinoe was a descendant of Alexander I of Macedon and thus a member of the Argead dynasty, claiming ultimate descent from Heracles. Ostensibly, Ptolemy's father was Lagus, a Macedonian nobleman from Eordaea, but many ancient sources claim that he was actually an illegitimate son of Philip II of Macedon. If true, this would have made Ptolemy the half-brother of Alexander. It is probable that this is a later myth fabricated to glorify the Ptolemaic dynasty.