Also, it probably helped that he was the the most educated of the Church Fathers. Ya know, being a Pharisee (I think) and all.
(Wait, was he a pharisee? I'm not sure).
According to Acts, he was a Pharisee, but only by definition of being the son of one. Initially having the Greek name Saul, he was not born in Israel, but rather in the city Tarsus in modern day Turkey, which was at the time Culturally Greek and nationally Roman.
He lived until his later life as violently opposed to the Judaism. It's early days, Christianity was equated with Judaism by outsiders. Everything changed when, as he was wandering around a road, and he claims to have suddenly seen Jesus in a flash of light. There is no evidence that Paul was even aware of Jesus prior to his death.
After this event, he immediately goes to Jerusalem. Or he doesn't. It depends on which part of the bible you're reading. There he starts preaching about Jesus, or again, doesn't, as the bible says he wasn't there when the bible says he was there.
Fourteen years after this first visit that may or may not have happened, he visits Jerusalem for the first time. In those fourteen years, we know absolutely nothing about what Paul was up to, other than presumably not being in Jerusalem.
Basically everything that Paul said during his preaching and letter writing campaign was interpreted as being the absolute truth from that point on, and he became second only to Jesus in terms of the formation of Christian thought.