Jeff Fortner is an agent with the CIA.
This is the CIA at the end of the 60s, solidly in the midst of the Cold War with the KGB, an agency seeing enemies spies behind every bush, probably because they were in fact there. No enemy plot was too outlandish to be true and vigilance was key. Which makes the trouble that Fortner encounters in the first recorded adventure rather interesting because the plot he uncovers is exactly what the doctor (or Director) ordered and no one wants to believe him.
Fortner is 28 years old when we first meet him. He is a decorated soldier from service in the Vietnam War which is still going strong as the stories take place in the late 60s to early 70s. He is a man who has paid his dues through at least two tours in that region as a member of the elite Marine Force Recon, including a brief period as a POW. When rescued by an experience CIA operative, he decides that going into that line of work was what he wanted to do. And this is despite the fact that his father, with whom he has a major conflict, is a now retired CIA legend. It is believed by many in the Agency that the younger Fortner got his start thanks to his old man. The truth is he got it despite the objections of the elder who has nothing but contempt for his son (long story, apparently).
The Fortner we meet is a man who has a quick temper and an inclination to punch people in the face or put them in a choke hold. This sounds like someone with too much aggression but since those "victims" tend to earn it by shoving guns in Fortner's face first, well, maybe his anti-social response is understandable. Over the course of the three books in the series, Fortner will age a bit and wisen a tad but he still likes to show his disapproval quite vigorously.