Saul of Taurius was a Christian persecutor; who was of the witnesses in the stoning of the first martyr, Stephen; who had been charged with blasphemy, after angering the greek-speaking Jews, or the Pharisees. After witnessing this, Saul continued to persecute Christians, and caused them more pain. But on a journey to Damascus his view and perspective changes, which is where I will pick up the story.
Saul and a group of men leave for Damascus to do some more persecuting when Saul is knocked off his horse by a light from Heaven. He is then spoken to by a voice from Heaven. The Lord, Jesus Christ asked Saul why he was persecuting him. Saul is terrified and astonished, of course. For a little while Saul contemplates everything that has happened, after he returns back to Damascus, and begins preaching about Christ, which he does for the rest of his life. Which is where he experienced his first time being persecuted by the people who were his allies; he barely escapes. He also begins his missionary journeys. He also changes his name to Paul(which I will now be calling him by).
He first went to Jerusalem which did not end so well, but that did not stop him, he became a preacher at Antioch. He traveled many miles, mostly on foot spreading the message of Christ; and that Christian messages were for everyone. He preached to gentiles(non-Jews), in Asia Minor and Greece; and traveled back and forth from countries including Italy, Asia Minor, Greece, Macedonia, and others. Although he established many churches and helped convert many people to Christianity, he suffered greatly from persecution, like many Christians did around that time. But that again did not stop him from preaching.
In summary: Paul started out as a person who persecuted Christians, but then after an incident that changes his life he begins for the rest of his life to spread the message of Christ, and to lead people to Him. He was a very important figure in the development of Christianity.