Andy Fisher is an agent with the FBI.
If you asked any of the agents who have worked with him, or worse, have tried to manage him, he is a very, very good agent who has an impressive list of arrests and convictions on his resume. This will be freely admitted but with a considerable amount of regret, frustration, or out-and-out snarls because as Fisher goes about his duties, he has a way of rubbing a lot of people the wrong way. It is not that he is disrespectful of authority per se so much as it is he often just lacks respect or refuses to show it.
The way this has gone in the many years he has worked as an agent (how many is not stated but he has clearly been around at least a decade if not more) is simple. If he has a question to ask, he asks it without fanfare or any real tact. Whether the person being questioned is a low-life purse snatcher caught red-handed or a high-level Cabinent official, the question would be phrased the same and if the answer did not come across as truthful, his response would not vary either. Fisher is not out to make enemies. He is also not out to make friends and keep from making waves. Fisher's attitude is that is someone has a problem with the way he does his job, that is indeed their problem, not his.
Fisher does have his share of problems with the world, though. This incredibly annoying insensitivity to his need for nicotine is proving almost intolerable. Fisher might be so bad a chain-smoker that he lights one cigarette with the previous one but he is darned close. He likes to smoke. He really likes to smoke. And it ticks him off when one place after another will invariably have someone telling him he cannot light up there. Especially New York. New York City's anti-smoking laws were specifically written to cause him trouble and he resents it. When given the chance to save NYC from a major disaster, he pondered, for a split second, what he should do. He saves the day but his dislike of their dislike of his habit remains.
Fisher also loves caffeine. Coffee is the drink of the gods, or it should be if they really are gods. Hot and black and as strong as can be made. Lots of it. And if it smells like and pours like crankcase oil, you might be getting it right. Let him have a cigarette with his coffee and you have earned his appreciation. Keep him for both and you must be working for the other side.
Take Fisher's love of coffee, his need for nicotine, and his habit of making smart remarks that go over well with the common guy but which irks the tar out of those full of themselves, all combine to make a good description of Fisher. Especially when you throw in an incredible ability to spot inconsistencies in a story or flaws in the logic of a case theory.
He is very good at his job. Since his job often involves going up against enemies of the US who come to America to hurt it, it is a very good thing for the country he is as good as he is.