According to the New Testament in the Bible, in the Book of Acts, Paul, once known as Saul, was a terrible persecutor of Christians.
In Acts 9, Saul is described as something of a "bounty hunter." He goes to the high priests to get permission—if he finds any Christians on the road to Damascus—to bring them back.
But Saul, still breathing threats and murder against the disciples of the Lord, went to the high priest and asked him for letters to the synagogues at Damascus, so that if he found any belonging to the Way, men or women, he might bring them bound to Jerusalem. (1-2)
The story of Paul's conversion is a famous one. Still known at that time as Saul, he traveled along the road to Damascus with his companions. All of a sudden, there was a great light and the voice of Jesus spoke to him, challenging him for his behavior against His followers—and therefore, against Christ.
…suddenly a light from heaven flashed around him. And falling to the ground he heard a voice saying to him, “Saul, Saul, why are you persecuting me?” And he said, “Who are you, Lord?” And he said, “I am Jesus, whom you are persecuting. (3-5)
Jesus' voice told Saul to go on to Damascus where he would receive word as to what was expected of him. However, though he eyes were open, he was blind, and his companions had to lead him to the city. There he waited for three days. He did not eat or drink.
Meanwhile, in Damascus, Jesus appeared in a vision to Ananias. He told him to go to a certain house where he would find a man of Tarsus, named Saul, who would be praying. And Saul would have had a vision of Ananias coming and healing his blindness. Ananias was fearful, for Saul's reputation has preceded him. Many knew of how much havoc he had wrought upon Jesus's followers. Ananias was afraid, too, because Saul had great political power and could have anyone arrested who followed "the Way." Jesus explained that he had great plans for Saul.
But Ananias answered, “Lord, I have heard from many about this man, how much evil he has done to your saints at Jerusalem. And here he has authority from the chief priests to bind all who call on your name.” But the Lord said to him, “Go, for he is a chosen instrument of mine to carry my name before the Gentiles and kings and the children of Israel." (13-15)
Ananias did as he is told and spoke to Saul:
Brother Saul, the Lord Jesus who appeared to you on the road by which you came has sent me so that you may regain your sight and be filled with the Holy Spirit. (17)
Immediately, the Scriptures say, Saul's eyesight was restored, as if "scales" had fallen from his eyes. Saul was baptized at that moment. He spent several days with the disciples, and began to proclaim that Christ was the Savior.
And immediately he proclaimed Jesus in the synagogues, saying, “He is the Son of God.” (20)
The people were amazed, knowing that prior to this Saul had actively persecuted the followers of Jesus. Saul's faith grew, and he preached even more on behalf of Christ. The change in him was miraculous, proving the power of Jesus. Soon the Jews planned to kill Saul, but the disciples helped him to escape from the city.