• Ptolemy (Ptolemaios) III Euergetes (Benefactor) (Πτολεμαίος ΙΙΙ Ευεργέτης)
• Ptolemaic King of Egypt with Berenice II
• Preceded by: Ptolemy II
• Succeeded by: Ptolemy IV

Ptolemy III Euergetes I, (Ptolemaeus III) (Evergetes, Euergetes) (246 BC-222 BC). The third ruler of the Ptolemaic dynasty of Egypt, he was the eldest son of Ptolemy II of Egypt Philadelphus and Arsinoe II of Egypt. He came to power in 246 BC upon the death of his father. He is most noted for his invasions of the northern kingdom of Syria which he commenced upon the murder of his eldest sister Berenice Phernophorus.

He married Berenice of Cyrene between 244/243 and they were parents of Arsinoe III of Egypt and Ptolemy IV of Egypt.

Canopus decree of Ptolemy III : proposal to add one day every four years to keep the festivals at the right time of the year (an advice probably from Eratosthenes)