Paul generally refers to Saint Paul, also called Paul of Tarsus or Saul of Tarsus. Paul is an important figure in the early church, according to tradition and the Acts of the Apostles he started off as Saul and persecuted the Christians but experienced a vision or Hallucination on the road to Damascus. After that he converted to Christianity and changed his name to Paul. Saint Paul became a Christian missionary and wrote many epistles though it is likely that Paul did not write all the epistles attributed to him.  Different texts in epistles attributed to Paul contradict each other and some may have been for specific early churches rather than for the whole of Christendom. 
There is a claim that some parts of Christianity originate from Paul and even conflict with the teachings of Jesus.  There is also a claim that Paul did not believe in an earthly Jesus. He didn't write about the virgin birth, place or time of birth, parents' names, childhood, John the Baptist or Jesus' baptism, the devil's temptation, moral teachings, miracles, apocalyptic views, transfiguration, Judas, Peter's denial, his arrest and trial, twelve disciples, the women who came to his tomb, Son of Man, travels, or parables. The few introductory lines in his epistles that do seem to imply an earthly Jesus are generally agreed by Bible scholars to have been written by somebody else and later appended to his letters.