Jake Grafton is an agent with the CIA.
He is also an officer in the U.S. Navy.
Really two series in one, the tale of Jake Grafton depicts the adulthood advance of a very tenacious and compelling character.
The first part, comprised of two non-spy novels, tells of the life of a Navy pilot during and immediately after tours in Vietnam. The stories are gripping and certainly autographical in nature as the author was himself a pilot in that conflict during two cruises with the USS Enterprise.
The second section comprise the international intrigue (i.e. spy) section. Grafton has been promoted to Captain and sees his career changing as he gets more and more involved in espionage matters. Never actually a spy himself, Grafton will engage in numerous adventures where spies fight with or against him.
The interesting aspect to the Grafton series is that they are not just centered around the intrigue - you get to see a well-rounded character with a life. He is even married and his wife, Callie, plays an important, albeit background, character at first but quickly becomes a prominent player in Grafton's work as well as his private life.
Each book sees progression in the life of the Graftons. He rises in rank and then retires. He takes a job with the CIA and moves up that chain of command, eventually reaching a position where he can sit with and advise the President and other government leaders.
After the tenth book, the author had taken Grafton perhaps as far as he felt reasonable for the action hero that he was. It no longer made sense for Grafton to be skulking into back rooms or down dark alleys quite as often as before. He was too public and well known. As a result, a new character was brought in as the main adventurer.
Tommy Carmellini now wears the literary trenchcoat but Grafton is still there in spirit and often in person. Tommy is a former thief and now a full-time agent with the CIA who is assigned to help Grafton on an assignment. After the two hit it off, he becomes the main agent Grafton asks for when important, dangerous work needs to be done. When Carmellini is not on an assignment, he helps run a locksmith shop with a genius in lock picking, an association that has come in handy on many occasions.