Paul the Apostle, originally known as Saul of Tarsus, was a significant early Christian missionary and theologian who played a crucial role in the spread of Christianity beyond Jewish communities into the Gentile world. His letters, known as the Epistles, form a substantial part of the New Testament and outline key Christian doctrines, emphasizing themes like grace, faith, and salvation. Paul's conversion experience on the road to Damascus marked a pivotal point in his life and the history of early Christianity, highlighting the movement's transition from a Jewish sect to a global religion.