Did Paul invent Christianity?

This idea has real defenders in the history of scholarship. It isn't the mainstream historical view today, though. The evidence points toward Paul inheriting and passing on beliefs that already existed before him, not creating them.

Paul himself explicitly says he "received" the core message he preached—that Christ died, was buried, and was raised. He didn't invent it. Most historians date that core summary to within just a few years of Jesus' death, before Paul was even writing.

Paul also describes personally meeting Peter and James, Jesus' own brother, in Jerusalem a few years after his conversion. James was already a recognized leader there, independent of Paul. The two sometimes disagreed—hard to explain if Paul had simply invented the whole religion himself.

Paul clearly shaped how Christianity spread and how it was explained to a wider world. Shaping something and inventing it from nothing are different claims. The earliest evidence supports the first, not the second.