As the gospels began to be studied by the Church Fathers, they recognised a literary dependency among the synoptic gospels, such that two of them must have been copied from the third, and came to the conclusion that Mark and Luke were copied from Matthew. The Church Fathers came close in their assumption, but biblical scholars now know that Mark's Gospel was the first New Testament gospel to be written, approximately 70 CE. Matthew and Luke were subsequent copies from Mark. The gospel now known as John's Gospel was also inspired by Luke's Gospel, with a small amount of material taken direct from Mark. Thus, the further removed from the original Gospel of Mark, the less accurately it depicts Jesus.
This leaves us to establish, as far as possible, how accurate the depiction of Jesus is in Mark's Gospel, and there is a surprising range of views as to the sources for this gospel. Raymond E. Brown (An Introduction to the New Testament) says that Mark seems to depend on traditions (and perhaps already shaped sources) received in Greek. Parallels have been detected between Mark and Paul's letter to the Romans and 1 Corinthians. It could be that Mark's author wove his gospel around various key people (principally James, Peter and John) and key events that he found in Paul's epistles. Dennis R. MacDonald (The Homeric Epics and the Gospel of Mark) also sees close parallels between the Gospel and Homers epics, which he believes Mark's author used as sources for many gospel passages. Certainly, the sophisticated chiastic structure of the Gospel means it could not have been a literal history of the life and mission of Jesus.
We can rule out the nativity accounts in Matthew and Luke, which biblical scholars regards as literary inventions. We can also rule out the four different depictions of the empty tomb and the appearances of the risen Jesus. Mark's Gospel originally ended at verse 16:8 with the young man telling the women that he is risen and they fled in terror, telling no one. The 'Long Ending' was added much later, after the other gospels had been written.