Celsus (Greek: Κέλσος) was a 2nd century Greek philosopher and opponent of Early Christianity. He is known for his literary work, The True Word (Account, Doctrine or Discourse) (Λόγος Ἀληθής), written about by Origen. This work, c. 177 is the earliest known comprehensive attack on Christianity.
According to Origen, Celsus was the author of an anti-Christian work titled The True Word. This work was lost, but we have Origen's account of it in his writings. It was during the reign of Philip the Arab that Origen received this work for rebuttal. Origen's refutation of The True Word contained its text, interwoven with Origen's replies. Origen's work has survived and thereby preserved Celsus' work with it.
Celsus seems to have been interested in Ancient Egyptian religion, and he seemed to know of Jewish logos-theology, both of which suggest The True Word was composed in Alexandria. Celsus wrote at a time when Christianity was being actively persecuted and when there seems to have been more than one emperor.
As an anti-Christian Greek philosopher, Celsus mounted an attack on Christianity. Celsus wrote that Jesus's father was a Roman soldier named Panthera. The views of Celsus drew responses from Origen who considered it a fabricated story. Raymond E. Brown states that the story of Pantera is a fanciful explanation of the birth of Jesus which includes very little historical evidence - Brown's analysis does not presuppose the doctrine of the "virgin birth," but cites the lack of historical evidence for Celsus' assertion. In addition, Celsus addressed the miracles of Jesus, holding that "Jesus performed His miracles by sorcery (γοητεία)":
O light and truth! he distinctly declares, with his own voice, as ye yourselves have recorded, that there will come to you even others, employing miracles of a similar kind, who are wicked men, and sorcerers; and Satan. So that Jesus himself does not deny that these works at least are not at all divine, but are the acts of wicked men; and being compelled by the force of truth, he at the same time not only laid open the doings of others, but convicted himself of the same acts. Is it not, then, a miserable inference, to conclude from the same works that the one is God and the other sorcerers? Why ought the others, because of these acts, to be accounted wicked rather than this man, seeing they have him as their witness against himself? For he has himself acknowledged that these are not the works of a divine nature, but the inventions of certain deceivers, and of thoroughly wicked men.
Origen wrote in 248, it was at this point that Origen brought to light again a book written in the days of Marcus Aurelius but still in circulation. Sometimes quoting, sometimes paraphrasing, sometimes merely referring, Origen reproduces and replies to Celsus' arguments. Since accuracy was essential to his refutation of The True Word, most scholars agree that Origen is a reliable source for what Celsus said.
Celsus shows himself familiar with the story of Jewish origins. Conceding that Christians are not without success in business (infructuosi in negotiis), he wants them to be good citizens, to retain their own belief but conform to the state religion. It is an earnest and striking appeal on behalf of the Empire, and shows the terms offered to the Christian sects, as well as the importance of the various sects at the time. It is not known how many were Christians at the time of Celsus but as a comparison the estimation of Wilken of the Jewish population of the empire to have been about 10% may be quoted. The Christians were certainly fewer. It is unlikely their influence was greater than what the physical evidence reveals throughout AD 100-400.