The Ptolemaic cult of Alexander the Great was an imperial cult in ancient Egypt during the Hellenistic period, promoted by the Ptolemaic dynasty. The core of the cult was the worship of the deified conqueror-king Alexander the Great, which eventually formed the basis for the ruler cult of the Ptolemies themselves. The head priest of the imperial cult was the chief priest in the Ptolemaic Kingdom.

An imperial cult is a form of state religion in which an emperor or a dynasty of emperors are worshipped as demigods or deities. "Cult" here is used to mean "worship", not in the modern pejorative sense. The cult may be one of personality in the case of a newly arisen Euhemerus figure, or one of national identity or supranational identity in the case of a multi-ethnic state. A divine king is a monarch who is held in a special religious significance by his subjects, and serves as both head of state and a deity or head religious figure. This system of government combines theocracy with an absolute monarchy.