J. C. Bannister is a contract assassin.
He prefers words like 'solutionist' which is an actual real word (I looked it up) but it is used far more often for people who solve puzzles, not people who kill people. Bannister's take on the matters is "Sometimes the solution to a person's problem is a dead body. Sometimes dead bodies occur on the path to said solution. But killing is rarely the goal. Solving the problem is."
Bannister is really good at solving problems. He modestly attributes his success to working "with a loose team of other specialists whose skills compliment my own. Where I have deficiencies, they have strengths, and vice versa". He further specifies to a client that he does not "kill indiscriminately. There are lines that I will not cross". He also informs that client that "I don't enjoy killing, but it is a marketable skill."
Bannister, six feet tall and in superb athletic condition, is a former Army Ranger who was taught how to kill by the military and more or less when to kill by the Agency. He learned how to make it all profitable mostly on his own.
He has three very close friends working with him and having his back and so much more. Duke, Joan, and Kowalski make up Bannister's team and together they are one heckuva force. There had been another member of the team, Gorman, but he had been killed in Indonesia just before the start of the first recorded adventured. The team has been operating quite successfully for several years (likely seven with Joan and three with Duke) by the time we first meet them.
Note that Bannister's membership in this compendium does not come from the fact that he is ex-CIA but because the problems to be solved by him and his team all fit firmly in the criteria. Invariably, it seems, at some point in each assignment Bannister will end up working either for an intelligence organization or against one.
Bannister muses to himself, "One of the rules of business all over the world - you don't have to like the client."