Jake Armitage is an agent with the NSA.
He is, actually, considered a contractor for that American intelligence organization. And by that term we really mean an assassin. His orders typically come from the very top of that department, the Director himself, who sends an encrypted message to a very private number, at which point Armitage knows where to do and who to eliminate.
From what he thinks about now and then, we learn that he has been doing this sort of work for quite a long time. It gets to him now and then, the loneliness. He muses regretfully that "he had no focus. No one to care about. One contract assignment blended into the next". Then he receives another call and decrypts another message and for a time he again has a goal.
From countless days in the field, Jake's stealth ability had reached legendary status. He reflects in a section right after we first meet him "just how many times the Russians had failed to capture him. In their own country." Before we let his head get too big, however, we will witness more than a few times that someone out to kill him will catch up with him and there will be considerable mayhem. To his credit, though, he walks (well, once in a while limps) away and his assailants do not.
In the second recorded adventure, Armitage is contacted by retired general working on behalf of the NSA to perform a job for them. Not unusual there, of course, except that it seems the general's invitation was in a round about manner - he hired several men he wanted killed to track down and kill Armitage, knowing they would fail and that Armitage would figure out who sent them and ... Like I indicated - unusual.