You asked: Was Paul the founder of Christian religion or Peter?
The Urantia Book credits both Peter and Paul in connection to the origin of the Christian religion. They both certainly had a lot to do with what happened. Here are two examples:
About Paul:
128:3.6 And this was the same Stephen who subsequently became a believer in the teachings of Jesus, and whose boldness in preaching this early gospel resulted in his being stoned to death by irate Jews. Some of Stephen’s extraordinary boldness in proclaiming his view of the new gospel was the direct result of this earlier interview with Jesus. But Stephen never even faintly surmised that the Galilean he had talked with some fifteen years previously was the very same person whom he later proclaimed the world’s Savior, and for whom he was so soon to die, thus becoming the first martyr of the newly evolving Christian faith. When Stephen yielded up his life as the price of his attack upon the Jewish temple and its traditional practices, there stood by one named Saul, a citizen of Tarsus. And when Saul saw how this Greek could die for his faith, there were aroused in his heart those emotions which eventually led him to espouse the cause for which Stephen died; later on he became the aggressive and indomitable Paul, the philosopher, if not the sole founder, of the Christian religion.
About Peter:
195:0.1 THE RESULTS OF Peter’s preaching on the day of Pentecost were such as to decide the future policies, and to determine the plans, of the majority of the apostles in their efforts to proclaim the gospel of the kingdom. Peter was the real founder of the Christian church; Paul carried the Christian message to the gentiles, and the Greek believers carried it to the whole Roman Empire.
And this one includes both men:
196:2.1 Some day a reformation in the Christian church may strike deep enough to get back to the unadulterated religious teachings of Jesus, the author and finisher of our faith. You may preach a religion about Jesus, but, perforce, you must live the religion of Jesus. In the enthusiasm of Pentecost, Peter unintentionally inaugurated a new religion, the religion of the risen and glorified Christ. The Apostle Paul later on transformed this new gospel into Christianity, a religion embodying his own theologic views and portraying his own personal experience with the Jesus of the Damascus road. The gospel of the kingdom is founded on the personal religious experience of the Jesus of Galilee; Christianity is founded almost exclusively on the personal religious experience of the Apostle Paul. Almost the whole of the New Testament is devoted, not to the portrayal of the significant and inspiring religious life of Jesus, but to a discussion of Paul’s religious experience and to a portrayal of his personal religious convictions. The only notable exceptions to this statement, aside from certain parts of Matthew, Mark, and Luke, are the Book of Hebrews and the Epistle of James. Even Peter, in his writing, only once reverted to the personal religious life of his Master. The New Testament is a superb Christian document, but it is only meagerly Jesusonian.
It appears to me that the teachings of The Urantia Book lean toward Paul as the real founder of Christianity, but they do give credit to Peter as well. And, in this last quote, it also appears that they may make a distinction between the origins of the Christian religion and the Christian church.
For more reading on this subject, here is our topical study about Christianity.
And, here are two TruthBook links that you might like to pursue. This one is the result of a search I did on Peter and Christianity
This one is the result of a search on Paul and Christianity.
These searches can give you a great deal more information about what The Urantia Book teaches regarding these two giants in the history of Christianity.
