Serapis, also known as Sarapis, is a captivating Graeco-Egyptian god that emerged during the third century BC. This unique deity was created on the orders of Ptolemy I Soter, a Greek pharaoh of the Ptolemaic Kingdom in Egypt. Ptolemy sought to unify the Greeks and Egyptians under his rule, and the cult of Serapis was established as a deliberate policy to achieve this goal.

The cult of Serapis was actively promoted by the Ptolemaic kings, leading to its widespread popularity during the Roman Empire. Serapis often replaced Osiris as the consort of Isis in temples outside Egypt. While Ptolemy I may have officially created the cult of Serapis and endorsed him as the patron deity of the Ptolemaic dynasty and Alexandria, Serapis was a syncretistic god that drew elements from the worship of Egyptian Osiris and Apis. Additionally, Serapis incorporated attributes from other deities such as the chthonic powers associated with the Greek Hades and Demeter, as well as benevolence derived from associations with Dionysus.

Iconographically, Serapis was depicted with a Greek appearance but adorned with Egyptian symbols. The imagery of Serapis combined elements from various cults, representing abundance and resurrection.

The Greeks held little reverence for figures with animal heads, leading to the selection of a Greek-style anthropomorphic statue as the idol of Serapis. This statue was proclaimed to be the equivalent of the highly revered Apis and was named Userhapi, meaning "Osiris-Apis." The Greek rendering of Userhapi became Sarapis, and it was believed to represent the complete form of Osiris rather than just his life force, known as ka.

The cult statue of Serapis erected by Ptolemy I in Alexandria reflected a combination of Egyptian and Greek styles. The statue portrayed a figure resembling Hades or Pluto, the kings of the Greek underworld. Serapis was depicted enthroned, wearing a modius—a basket or grain-measure—on his head, symbolizing the land of the dead according to Greek tradition. The scepter held in Serapis' hand denoted his rulership, and at his feet rested Cerberus, the gatekeeper of the underworld. A serpent, representing the Egyptian symbol of rulership, the uraeus, appeared at the base of the statue.

The etymology of Serapis can be traced back to the syncretic worship of Osiris and the bull Apis in ancient Egypt. Originally known as wsjr-ḥp in the Demotic script, meaning "Osiris-Apis," the name was later written in Coptic as Userhapi. The Greeks adopted an alternative form, Sorapis, which was later modified to Serapis. The name variation Serapis gained prevalence during Roman times.

Serapeia, the temples or religious precincts devoted to Serapis, were established throughout the ancient world. The most renowned Serapeum was located in Alexandria, Egypt.

Evidence suggests that the cult of Serapis predated the Ptolemaic rule in Alexandria, as a temple of Serapis is mentioned in 323 BCE by both Plutarch and Arrian. However, it was Ptolemy I Soter who made significant efforts to integrate the religious beliefs of the Greeks and Egyptians. By erecting a statue of Serapis in Alexandria, Ptolemy aimed to create a deity that would earn the reverence of both groups. Plutarch recounts a tale in which Ptolemy stole the cult statue from Sinope in Asia Minor. In a dream, he was instructed by an "unknown god" to bring the statue to Alexandria, where it was pronounced to be Serapis by two religious experts—an Eumolpid (a member of an ancient family involved in the Eleusinian Mysteries) and the Egyptian priest Manetho. This tale, however, may contain inaccuracies, as some Egyptologists believe that the "Sinope" referred to is the hill of Sinopeion, the site of the pre-existing Serapeum at Memphis.

Serapis, along with his wife Isis and their son Horus, gained prominence in the Greek world. Pausanias, in his 2nd-century CE work "Description of Greece," mentions two Serapeia on the slopes of Acrocorinth above the rebuilt Roman city of Corinth, as well as one at Copae in Boeotia.

The cult of Serapis spread throughout the Roman Empire, and Serapis was sometimes equated with Anubis, the Egyptian god often identified with Cerberus. The Iseum Campense in Rome, a sanctuary dedicated to Isis, included worship of Serapis. Serapis even appeared on imperial coinage alongside reigning emperors.

However, with the rise of Christianity, the cult of Serapis, like many pagan cults of the time, experienced a decline. Emperor Theodosius I implemented religious laws that aimed to suppress paganism in the empire. The main Serapeum in Alexandria survived until the late 4th century when it was destroyed by a Christian mob led by Pope Theophilus of Alexandria during one of the frequent religious riots in the city.

In popular culture, Serapis has made appearances in various works. In the Asterix franchise, Serapis is one of the gods invoked by Egyptians, similar to how Gauls invoke their own deities. Serapis is also a key antagonist in the Rick Riordan short story "The Staff of Serapis," which combines elements from two of Riordan's major series, The Kane Chronicles and Camp Half-Blood Chronicles.

In conclusion, Serapis represents a remarkable fusion of Greek and Egyptian deities. The cult of Serapis played a crucial role in uniting the Greeks and Egyptians under the Ptolemaic rule in Egypt. Serapis's iconography blended elements from various cults, symbolizing abundance and resurrection. Although the cult of Serapis flourished during the Roman Empire, it ultimately faced decline due to the spread of Christianity. Today, Serapis continues to captivate through appearances in popular culture, keeping alive the legacy of this intriguing Graeco-Egyptian god.