Julius Caesar had enlarged the boundaries of what was to become the Roman Empire and he became Rome's first absolute ruler. The Roman power was secure and its military power unchallenged. Christianity further began to grow and expand unlike previous religions. It took root in the Middle East and spread to Greece and Egypt.

Saul was born in Tarsus, which is now southern Turkey. He was a tentmaker by trade, and also studied philosophy in Jerusalem, and spoke several languages including Greek.

At first Saul was quite hostile towards Christianity, but after the crucifixion of Jesus Christ, Christ appeared to him in a vision while he was riding to Damascus. He was converted to Christianity on the spot and Saul changed his name to Paul and answered Christ's call to preach His word to the world.

Paul went to Jerusalem, and met Christ’s disciples Peter, James, and Barnabus (Galacians 1:18,19). It was during this and subsequent meetings they worked out a plan to spread out Christ's teachings in the Middle East and beyond. For the next 10 years Paul alone or with Barnabus he travelled to Tarsus, Greece, Macedonia, and Cyprus to establish churches. In Corinth he spent 18 months around 58 AD. It was here that he wrote his Letters to the Corinthians, detailing the Christian doctrine.

Over the next several years Paul’s success angered the Jewish and Roman authorities, because he had converted both Jews and non-Jews to Christianity. Here Paul entered a debate, and he was jailed for 2 years.

Upon his release he went to Rome he met St, Peter, the hand-picked successor of Jesus, and was welcomed in the Christian community where he spent 2 fruitful years writing and lecturing. Then he was planning a trip to Spain, but he probably was arrested and executed by the emperor Nero (37-68 AD).

St Peter was the first Pope of the Christian Church. St. Paul was after Jesus was the most influential  figure in the establishment of Christianity and the systematic foundation of the Christian doctrine.

Reference:

100 Men Who Shaped World History by Bill Yenne,
Gemini Books, New Delhi, 1997.