Depicted as a mature bearded man, the god Serapis is similar in appearance to Graeco-Roman gods like Zeus or Jupiter, with whom he shares the role of king of the gods. The stylized modius or grain measure on his head emphasizes his role as a fertility deity. The Greek god Hades also wore this symbol, linking Serapis with the role of god of the Underworld.
Serapis was a creation of the Ptolemies, the Greek rulers of Egypt from 323 to 30 B.C. They needed a deity to help unify the mixed population of native Egyptians and Greek colonists. Serapis blended aspects of major Greek and Egyptian gods, making him acceptable to everyone. For Egyptians, he was the god Osiris under another name. Most importantly for the Greeks, the new god had human form. The Greeks as well as the Romans found the Egyptian worship of deities in animal form disturbing. When Octavian, the future Roman emperor Augustus, visited Egypt, he curtly refused to pay his respects to the bull-god Apis, from whom Serapis also derived, saying that he was "accustomed to worship gods, not cattle."