Who, after persecuting christians, converted and became one of christianity's early proponents and writers?

   Apostle Paul

Explanation:  The apostle Paul, who, before becoming a Christian, was called Saul, and was a fierce persecutor of Christians. The very fact that he persecuted Christians indicates that Paul was not one of Christ's closest disciples, but immediately after the dissemination of Christ's teaching began, Paul, then still Saul, experienced enlightenment. It happened on the road to Damascus, in another of his persecutions of Christians when, according to the Bible, Christ Himself appeared to Paul, after which Paul was blinded for a short time, then experienced enlightenment and converted to a Christian. So Paul's conversion can be thought of as early in Christianity. Paul was one of the most ardent Christians in the world, known for his epistles and conversion of Gentiles.

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