John Rexford is an agent with the CIA.
"To most people, Maj. John Rexford is a retired Marine living in the Catskill Mountains of New York on disability. Even John’s girlfriend, Maggie, has no idea he’s really a CIA spook recruited in Afghanistan and assigned to kill enemies on US soil."
A couple of things we know right off. He is said to possess "exemplary skills in hand-to-hand combat and small arms weaponry" and he is a devoted cyclist in excellent shape. Both will prove useful in his endeavors.
John's Italian mother's coloring, combined with light brown eyes "allowed him to blend in with Middle Eastern, Mediterranean, or South American cultures, so long as he maintained a good tan". That tan proved not an issue because as we meet him, he has spent the last seven years in the Afghanistan mountains.
Before his career with the Agency, Rexford was an All-American tight end for Rutgers's football team, taken in the third round of the NFL draft. He chose instead to join the military and serve in the Middle East. He said he had realized that as fast and agile as he was, and he was exceptional, being 5'9 at 165 lbs meant it was more likely he would have sat on the bench for a few years and then "as soon as my spikes hit the turf, they would have crippled me".
Having decided to serve in the military, Rexford chose the Marine Corps. When we meet him he has risen to the rank of Major. "He was one of a handful of Marine Scout Snipers ever to have passed the strenuous Delta Force commando qualifications. Immediately afterward, he was deployed to Afghanistan where the CIA's highly secretive Special Activities Division's (SAD) elite Special Operations Group (SOG) assigned him a handler. Major John Rexford was given a code name, removed from his squadron designation as a Scout/Sniper, and left to work alone in the mountains of northeastern Afghanistan. There are approximately one million four hundred thousand people on the US military active-duty list. His skill set made him statistically better than one in a million."