Who is Josephus from Jesus: A Revolutionary Biography and what is their importance?

Josephus was a Roman historian whose records of the time at which both Jesus and John lived, as well as of the years following their deaths are used both in "Jesus: A Revolutionary Biography" and other historical analyses as the primary source material. The author goes to pains to point out that while Josephus and his writings were unarguably influenced by the social and political circumstances in which he lived and wrote, a great deal of what he includes in his work can be seen as having a significant degree of accuracy. In other words, he and his work are seen as accurately representing the circumstances of the time in which Jesus lived, taught, and died.