Is contemporary evidence required to establish the historicity of a person from ancient history, such as Jesus Christ or Alexander the Great? I was wondering if contemporary evidence (besides the Bible) is required to establish authenticity of an ancient historic figure.
I suppose that whether contemporary evidence is required will depend on the person who is asking. It just so happens that several non-Christian historians in the late first and very early second century mention Jesus. These include Josephus, a Jewish historian, as well as Tacitus, Seutonius, Pliny and other Roman historians. If you go to my web site, in the Power Point section you will find a power point titled "Jesus and Christian Apologetics." This power point lists most of the actual references by non-believers to Jesus. In fact, we have the same number of authors (not even counting the dozens of Christian writers!) who describe Jesus as we do authors who mention the emperor Tiberius, who ruled at the time Jesus was killed. That Jesus was a real historical figure is established beyond any reasonable doubt at all. I would say the fact that he lived is established almost as well as the fact that Alexander the Great lived.
Having said that, I believe that Moses and Abraham lived as well. Our hard evidence for these two extremely important Bible characters is much less. Both were members of a relatively insignificant group who were primarily nomadic, so we can expect very little physical proof of the events of their lives. In both cases, we are reliant to a significant extent on the reliability of the Old Testament as history. I believe the Old Testament is, by far, the most reliable historical document of the ancient world. If you do not understand why I make that claim, I suggest you listen to a recent class I taught on history, archaeology and the Bible. It is available in the Evidenceforchristianity story in the history and archaeology section. It is an APLA class as you will see. Also, there is a nice power point at my web site on history, archaeology and the Bible. You might want to check that out. Because the Old Testament has proven itself to be very reliable, at some point I believe we are justified in more or less assuming that if it mentions a particular person, then that person lived. I also believe the OT is inspired by God, which makes me even more strongly confident of the historical accuracy of the Old Testament. You should investigate this for yourself, but I believe you will agree when you do.