Who was Celsus, and why did Origen write Contra Celsum in response to him?

Celsus was a 2nd-century Middle Platonist philosopher and a prominent critic of Christianity. He is best known for his work Alēthēs logos ("The True Doctrine" or "True Word"), in which he dismissed Christianity as a crude, bucolic assault on the intellectual values and religious traditions of classical culture.12

Origen wrote Contra Celsum in approximately 248 CE at the request of his patron, Ambrose, to provide a systematic defense of the faith against Celsus’s attacks. Origen’s response was motivated by several key factors:1

• Intellectual Vindication: Origen sought to demonstrate that the Christian faith was not merely a prejudice of the unreasoning masses or a refuge for social outcasts, but a belief system compatible with a philosophic mind.1
• Refuting Pagan Criticism: He aimed to counter Celsus’s characterization of Christianity as an irrational threat to the established order and classical culture.12
• Philosophical Engagement: While both men shared basic Platonic presuppositions, Origen used the work to argue for the legitimacy of thinking within a Christian framework, effectively formulating a classic early Christian defense against the "cultured despisers" of the era.12