Stone Waverly is an agent with the CIA.
When we first meet him, he has been an agent/analyst with the Agency for just over 20 years, being just over 50 years old when the first recorded adventure takes place in the early days just after 9/11.
Thanks to a joint meeting he was ordered to attend and at which he was directed to give a quick synopsis of his background, we know that he graduated from the University of Arkansas with a History degree minoring in U.S. military history. Through ROTC he became a lieutenant in the army when he got out of school and went into the Rangers where he got his first taste of the clandestine world through a small surveillance contingent in that group. Since it was now peace time and he knew his chances for advancement were limited, Waverly was planning to leave the service after his commitment was up to return home but the CIA came calling.
The CIA offered him a chance to join a new unit which was consisting of ex-servicemen to work "as a sort of paramilitary surveillance and enforcement arm" of Langley to "mount clandestine operations against terrorist organizations that were perceived to be a threat to the United States".
He worked with the Mujahideen in Afghanistan against the Soviet forces there, even helping set up the cave complexes in Tora Bora. After the Russians withdrew, his career took him to India, Pakistan, and Northern Iraq. Since 1994 he worked at the headquarters of the CIA as the team leader of the counter-terrorism group.
Though many people might be, at that point in a career, thinking about retiring to something else, Waverly is about to see his life take a very interesting and very challenging change of direction.