Josh Fallon is an agent with the CIA.
At least he is when the series starts and he has been one for a few years. Before that he was a proud member of the elite U.S. Army Rangers where he was rated one of their best snipers. We learn that after the Rangers, Fallon was for a while a member of the FBI's SWAT team, though we do not know how long he was with them. As the series progresses, he will transition from the Agency to private security work. It is obvious that Fallon likes a challenge and even more so that he does not like sitting still for long.
All this time, he performs his missions admirably but invariably causes some new enemy to become very unhappy with him, always in a way that makes sense and comes across, unfortunately for him, reasonable. Since it usually takes some time to prepare an offensive, the retribution does not come immediately but takes a while to grow and fester and to give Fallon a chance to think life might have gotten back to something resembling normal.
Speaking of normal, as it says in his first recorded adventure, normal, or average, is the way people who do not know him would consider him. "If someone described him, they would say he was, well, they would say - average. Average height, average weight, average build, maybe perhaps a little on the lean side now. Average color hair and his eyes? That may be where they differ in opinion. His eyes were grey, but that's not what others would say. They would describe his eyes as warm, friendly, cold, hard, quiet, sparkling, listening, hurt, lively, and more. The eyes were the window to the soul and Josh Fallon's eyes showed many souls - whatever soul he chose to show. Of his many chameleon-like qualities, that was his best. And in his chosen work, a necessity."