Alex Thompson is an historian.
Specializing in war related matters, he has become an expert in ferreting out war criminals by methodically tracking down every clue and combining them with his own inherent understanding of combat and its aftermath.
Thompson is a former Green Beret who saw considerable action in Vietnam, experience that would change his life. He learned how to kill and he learned how to avoid getting killed and he learned that neither was the kind of life he wanted. After leaving the military, he returned to school and worked hard to get his doctorate in History because the things he saw done in Vietnam made a lasting impression and made him want to learn if those actions were unique to that conflict or were representative of war in general.
His life then became quite mundane and peaceful as he spent the next ten years in basements and libraries, working on grant money to become a respected and published modern day historian. It was when the grant money started to run out and he needed to find a new source of income to fund his continued work that his life took another change, back to one of action, danger, and the heat of battle. Knowing that finding yet another grant was unlikely because the people who gave out grant money were no longer interested in Nazi war criminals.
When he was given the name of Nathan Cassierer, an eighty-year old financier who was born in Germany but who fled to England as WWII started and who was determined to hunt down as many Nazi criminals as he could before he died.
Thompson the Historian was not out to be an avenger or a policeman. He wanted to study war and war criminals in general. Once he joined with Cassierer, however, what he wanted no longer mattered. Staying alive became top priority.