In the early centuries of Christianity, there were over 200 Christian gospels in circulation, all of them containing wildly varied stories and theologies. As the Church became organized there was much worry that no-one truly knew what Jesus had said or done, so they settled upon a choice of just four Gospels: They picked the number four because "there were four winds, four points of the compass, four corners of the temple", mirroring the arguments of Irenaeus in the 2nd century - "just as the gospel of Christ has been spread by the four winds of heaven over the four corners of the earth, so there must be four and only four Gospels". The four canonical gospels comprise of the first three synoptic gospels, Matthew, Mark and Luke, which give a sometimes-consistent description of Jesus, plus the fourth one, John, which is radically different to the others. None of the gospels are eye-witness accounts of Jesus' life, and, they are all written in Greek and not in the native tongues of anyone who met and followed Jesus. Many of the stories in the Gospels are copied from Greek god-man legends, especially those of Dionysus and Osiris. Although we now know them by the names of Matthew, Mark, Luke and John, they are all originally anonymous.
Mark is the earliest gospel, composed between 60 and 80CE, by a Roman convert who was unfamiliar with Jewish customs and who had not met Jesus - the convert probably came to Christianity after St Paul (or his followers) had begun to preach to the gentiles (non-Jews). The oldest versions of Mark all ended at Mark 16:8 with the words "according to Mark", and an unknown author at some point added Mark 16:9-20.
Matthew and Luke both used Mark very heavily as their source material (92% and 54% copied, respectively), except they corrected many of his blunders about Jewish life and added additional material from a second source document that historians call "Q". There is only a small amount of material in Matthew and Luke that simply looks like the insertions of their own stories and ideas. Matthew was written after 70CE and definitely before 100CE. The first two chapters of Matthew were not present in the first versions and were added later by an unknown author. Luke was written after 93CE and also uses Josephus's Jewish Antiquities as a reference. It claims to have been written by a travelling partner of Paul but the text contains too many mistakes with regards to Paul, and was written too late, for that to be true. Matthew and Luke copied such a large portion of Mark, and both used extensive text from Q, that it is clear neither were eye-witnesses, or friends-of-eyewitnesses, of Jesus or of his disciples or of Paul.
Finally, John was written last. Our earliest fragment of it dates from 125CE, and all of the times it quotes Jesus it has Jesus speak using completely different conventions, sentence structures and a different style to all of the other gospels. Most people assume that John was a symbolic and figurative writer who was attempting to record history, but merely attempting to write interesting and meaningful stories about Jesus, who was by then, famous, and it is considered the least trustworthy of all the gospels.