Zack Matteson is an agent with the CIA.
Right off the bat I want to make sure you know that the story that is the life of Zack Matteson is totally and completely enmeshed with that of , a former CIA agent who had been Matteson's partner for many, many years before Scott (Flenn's first name) had "given up being an agnostic to become a priest, of all things!" That had been about a decade before we first meet either of them so they had very much gone their separate ways.
While Flenn had become an Episcopalian priest, Matteson had tried marriage to Donna but that hardly lasted very long and since then, Matteson had kept the number of people he was close to down to a bare minimum. "He'd come to prefer a life of bourbon, one-night stands, and chasing after bad guys." He was pretty good at all three.
Matteson is 46 years old at our introduction but still in trim, muscular build which he proudly and steadfastly maintains, despite the affinity to alcohol. Still have jet-black hair even after all the crazy scrapes he had found his way into and out of, he enjoys ocean-blue eyes and apparently so do the ladies. He also adores jellybeans, except the licorice ones, and always seems to have a bag of them with him; those black ones he just tosses away.