Erik Chatham is an agent for the CIA.
To most people, though, Chatham is a mercenary, a highly-paid soldier of fortune who will go wherever to fight whomever for the right price. He is good enough to command a very good salary. Whether it is service in Northern Africa, Central Africa, or the jungles of the Far East, he is a trained killing machine.
He is also a deep-cover operative for the CIA, specifically assigned to their Special Executive section. Described as the point of the lance on any operation, these are the people who are sent in to the most dangerous of situations, usually acting on their own with no hope of rescue by the cavalry. Trained to the utmost for survival, their high attrition is due to great danger they are involved in, not a lack of skill.
Chatham, who stands 5'11" with brown hair and a rugged face, is a veteran of many combats before the start of the series. Born and raised in middle America, he was called to service during the Vietnam War where his superiors recognized in him an affinity for fighting. This ability did not extend to traditional warfare as would have been practiced by Caesar, Napoleon, or Patton, but guerilla fighting as used by native Americans, the Viet Cong, and rebels like Che. With that form of combat, Chatham proved to be a natural.
It was while in Vietnam that his talents were noticed by the Agency and they recruited him without hesitation. Considering his expertise, his best use was in war-torn regions where a mercenary could pass without particular notice and Chatham has been working in that role for several years.
Chatham has more than a few scars for the many years of fighting he has done. He smiles ryely, though, when he thinks that his most obvious scar, one that runs from the corner of his right eyebrow halfway down his cheek, came from a car accident in Illinois when he was 17. If others wanted to think it was a reminder of a harrowing knife fight, who was he to correct them. That is the type of sardonic humor that Chatham carries with him, also evidenced by an exchange in which he makes a comment to a senior officer, the officer tells him that some people would not be pleased to hear him say such words, to which he replies, "I don't say them around some people."
If military action, especially troop-level, crawl through the swamp style, is your interest, this series is definitely one for you. The assignments Chatham get are not of the secret document courier duty or defector protection. He gets the overthrow a dictatorship kind of assignments, and does so from the field, not the office.