To what extent is there a "Search for Paul"? I am curious as to what historical evidence there is of Paul's life outside of his writings and, particularly, what skeptics have to say about what motivated Paul if he was not, indeed, divinely inspired.
Your question is very perceptive. Christianity derives a considerable part of its doctrinal content from the writings of the Apostle Paul. In the early 1800s, some scholars, especially in Germany, attempted to deny the Pauline authorship of the writings attributed to him. However, the evidence for Paul's historical existence and the consistency of the presentation of thought in his writings have convinced the majority of modern scholars that there was indeed an Apostle Paul and that he is responsible for the writings attributed to him. Today, some scholars object to crediting certain of these writings to Paul on various grounds, but there is little discussion about the historicity of the Apostle Paul and the profound impact of his ministry on the development of Christian theology.
Some of the more convincing evidence for the Apostle Paul's existence is found in the following ancient literature. Clement of Rome cites Paul in his letter to the church at Corinth (c. 95 C.E.). Irenaeus (140-202 C.E.) cites Paul in his work "Against Heresies." There is also a description of Paul's physical appearance in the apocryphal work "Acts of Paul and Thecla." Then, of course, there is Peter's reference to Paul in 2 Peter 3:15 and Luke's discussion of Paul's ministry in the book of Acts.
Many of the same German scholars who sought the "historical Paul" also attempted to understand the motivating force behind his writings. Some saw Paul's work as an attempt to Hellenize, or create a Greek expression of, Christianity. Others saw Paul's motivation for his work deriving from his conviction that before the Jewish people would come to accept Jesus, the gentiles must first be won. Others have sought to identify various unifying elements within his writings that provided the foundational starting point for all his work. However, no argument to date is as satisfactory as the most obvious one: Paul was called by God and inspired by the Holy Spirit to transmit many of the most profound theological revelations ever made known to humanity.