On occasion I've read someone who claims that Christianity is an invention of the apostle Paul. Here is why that idea is a bad one, from Richard Bauckham's Jesus: A Very Short Introduction. BTW - Bauckham's little book is a must-read for all interested in the historical Jesus.
Now, a lot of quoting from Bauckham... (it's worth it):
"It is important to realize that there was never a time, after the death of Jesus, when his followers regarded him simply as a teacher who had died a martyr’s death and left them his teaching to live by. From the 19th century onwards, there have been recurrent attempts to cast the apostle Paul in the role of founder of Christianity. Paul, it is suggested, was the first to make Jesus the object of faith and worship. But all such theories founder on the fact that, apart from anything else, Paul did not have sufficient power and influence to invent Christianity. After coming to believe in Jesus the Messiah, Paul was a major Christian missionary, who did much to spread the Christian Gospel, especially among non-Jews, in the areas of modern Turkey and Greece. But there was already a large Christian community in Rome long before Paul visited the capital. Christianity must soon have spread to Egypt and to Mesopotamia, developments with which Paul had no involvement. Because the second half of the Acts of the Apostles, the only narrative we have of the early spread of Christianity, focuses on Paul’s missionary travels, it is easy to get an exaggerated sense of their scope. Paul’s letters, also preserved in the New Testament, are among the most impressive early expositions of Christian faith and influenced the later church immeasurably, but it was several decades before they circulated outside the churches Paul himself founded. The centre from which the early Christian movement developed and spread throughout the ancient world was not Paul, but the Jerusalem church, led initially by the twelve apostles and subsequently by James the brother of Jesus. What was common to the whole Christian movement derived from Jerusalem, not from Paul, and Paul himself derived the central message he preached from the Jerusalem apostles. The heart of Paul’s teaching was common early Christian faith, though he was undoubtedly a thinker of genius who shaped that faith into a characteristic form, as did a number of other major teachers in the early church (such as the author of John’s Gospel).
It was not Paul who made Jesus the object of Christian faith and worship. He is this in a variety of early Christian writings that were not influenced by Paul. Already, in the early Jerusalem community, Jesus was understood to be a living agent, not just a figure of the past. Though they continued to participate faithfully in the worship in the Temple in Jerusalem, these early believers also met to ‘break bread’, which meant to continue the table fellowship with Jesus that his disciples had enjoyed during his lifetime. Here his sacrificial death was remembered and appropriated. Here, he was addressed in prayer and even worshipped. This was an extraordinary development in a thoroughly Jewish context, for it was the first principle of Jewish faith that only the one God may be worshipped. Many scholars are therefore reluctant to conclude that the earliest Christians worshipped Jesus. But it was an understandable consequence of their belief that Jesus now sat at the right hand of God on the heavenly throne. This made him a participant in God’s own unique sovereignty over his creation. Worship of God the only ruler of all things could now include worship of Jesus who shared that rule." (pp. 110-112)