Sergius Paulus was the proconsul (a Roman governor) of Cyprus. In Acts 13:7, Luke describes him as a "man of intelligence." Paul and Barnabas visited the city of Paphos in Cyprus during their first missionary journey. Paphos was where Sergius Paulus lived and worked. While they were there, they met a Jewish false prophet and sorcerer named Bar-Jesus (also called Elymas), who tried hard to stop the proconsul from hearing the gospel message.
Paul rebuked Elymas and cursed him with blindness. When Sergius Paulus saw what had happened, he believed the gospel message of Paul. This made him the first recorded person to become a Christian during Paul's first missionary journey.
t is at this point in the Bible that we see the name Saul change to Paul. Origen (an early Christian scholar) and many others since his time have thought that Paul changed his name to honor this important convert.