Who is Don Wolfe from The Tears of Autumn and what is their importance?

Don Wolfe is a British-speaking agent who Paul Christopher finds working next door to Barney Wolkowicz in Saigon, Wolfe recalls events in Mexico City when Lee Harvey Oswald visits in September 1963. There are no Vietnamese in Mexico City at that time, but a Cuban who is in transit from or to Vietnam, Manuel Ruiz.