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.