Who is Aaron Jastrow from The Winds of War and what is their importance?

Aaron Jastrow is the author of "A Jew's Jesus". He resides in a villa in Siena by choice, but when Germans begin killing Jews, Aaron finds that there is a problem with his passport. Jastrow doesn't seem overly concerned with the problem, but over time he becomes desperate. Unfortunately, red tape keeps him in Siena long past the time in which it is safe to be there.