Serapis or Sarapis is a Graeco-Egyptian deity. The cult of Serapis was promoted during the third century BC on the orders of Greek Pharaoh Ptolemy I Soter of the Ptolemaic Kingdom in Egypt as a means to unify the Greeks and Egyptians in his realm.

The cultus of Serapis was spread as a matter of deliberate policy by the Ptolemaic kings. Serapis continued to increase in popularity during the Roman Empire, often replacing Osiris as the consort of Isis in temples outside Egypt. Though Ptolemy I may have created the official cult of Serapis and endorsed him as a patron of the Ptolemaic dynasty and Alexandria, Serapis was a pre-existing syncretistic deity derived from the worship of the Egyptian Osiris and Apis and also gained attributes from other deities, such as chthonic powers linked to the Greek Hades and Demeter, and with benevolence derived from associations with Dionysus.