Jeremiah Flynn is an agent with the CIA.
He is, in fact, probably their very best agent, a man they can and do throw into a nasty situation with little intel and less backup and expect him to save the day. Well, sometimes they expect that favorable result and other times, it seems, they just toss and hope for the best.
Flynn is a terrific operative without a doubt. He is that because he is smart, resourceful, athletically gifted, and most of all, he loves his work. He will tell you over and over that he does not and that he would love to quit the Agency but truth be told, he cannot live without the thrill of pitting oneself against a dangerous enemy with the stakes crazy high.
Speaking of quitting, he sort of does that a couple of times and once or twice his bosses more or less quit him but then the world forces things back into place and another mission ensues.
Some say, incorrectly, that Flynn is successful because he has friends in high places. They allude to the rumored (and true) affair Flynn had with a newly elected and drop-dead gorgeous first female Vice President. Their facts about it helping his career are far from true, though. Make friends with someone powerful and you also make a lot of jealous enemies and affairs usually end, seldom for the better.
So along with a lot of very naughty people and groups out in the world that Flynn has to fight and vanquish, he has a host of troubling peoples behind him loving the chance to stab him in the back - or throw into a dark cell and then do the stabbing.