St. Paul the Apostle (שאול התרסי Šaʾul HaTarsi, meaning "Saul of Tarsus", Σαουλ Saul and Σαῦλος Saulos and Παῦλος Paulos ), the "Apostle to the Gentiles" was, together with Saint Peter and James the Just, the most notable of early Christian missionaries. Unlike the Twelve Apostles, there is no indication that Paul ever met Jesus prior to the latter's crucifixion. According to Acts, his conversion took place as he was traveling the road to Damascus, and experienced a vision of the resurrected Jesus. Paul asserts that he received the Gospel not from man, but by "the revelation of Jesus Christ".

Fourteen epistles in the New Testament are traditionally attributed to Paul, though in some cases the authorship is disputed. Paul had often employed an amanuensis, only occasionally writing himself. As a sign of authenticity, the writers of these epistles sometimes employ a passage presented as being in Paul's own handwriting. These epistles were circulated within the Christian community. They were prominent in the first New Testament canon ever proposed (by Marcion), and they were eventually included in the orthodox Christian canon. They are believed to be the earliest-written books of the New Testament.

Paul's influence on Christian thinking arguably has been more significant than any other New Testament author. His influence on the main strands of Christian thought has been demonstrable: from St. Augustine of Hippo to the controversies between Gottschalk and Hincmar of Reims; between Thomism and Molinism; Martin Luther, John Calvin and the Arminians; to Jansenism and the Jesuit theologians, and even to the German church of the twentieth century through the writings of the scholar Karl Barth, whose commentary on the Letter to the Romans had a political as well as theological impact.