Micah Dalton is a "cleaner" for the CIA.
Attached to the Agency's Clandestine Services, it is his job to come in and clean up after the mistakes of others. He is very good at his job but, as the series opens, he is suffering from a personal tragedy that has him drinking far too much, smoking too much, and not really caring about himself. As yet his work has not been affected but the rest of his world has suffered and it appears just a matter of time before his demons get the best of him.
Dalton is not a maverick per se but he is fiercely self-reliant, an attitude that took into the military's Special Forces and then into the CIA. He is comfortable working along but on his own, his actions can be confusing to others and sometimes give a false reading. It is not something that Dalton cares about but something he has to deal with.
As the series progresses, the friends that Dalton makes stay active participants in his adventures, making for an excellent continuity. These people first ponder his sardonic sense of humor, then look at the level of violence he routinely causes, and eventually come to their own understanding of Dalton. And still like him. They may not want him around at times but they still like him.
The enemies that Dalton makes, if they remain alive long enough, learn that Dalton has a very good memory and little compunction about going after them. When they need killing, Dalton usually accommodates them. This does mean he is rash, however. He thinks quickly and thoroughly and then reacts quickly and deadly.
One final interesting point about Dalton is that, due to an attempt on his life very early in the first book, he is prone to seeing mirages for a while. This clears up except for the repeated appearance of his old friend and teacher, Porter. Porter is dead. Dalton knows that well having discovered his mutilated body. But Porter shows up on occasion with a drink in his hand and an attitude. He jokes with Dalton and hassles Dalton and helps Dalton work things out in his head. Dalton is quite open with a few friends about seeing Porter and admits that while he does not believe in ghosts, he is not 100% convinced that Porter is not really there. Certainly Dalton enjoys the chats.