Dylan Hunter is an investigative reporter.
Really. That is what he does for a living.
What he does when not on the job is, though, what he really does. He hunts down those that seem beyond the ability of the system to bring to justice. The adage that power corrupts is proven over and over and often there is no one that can find a way to stop it.
Hunter should know. As a reporter he sees it. He writes about it so other people can see it. Then everyone moves on to the next story and the bad guy gets away with it. Except for when Hunter does not move on. Then the bad guy finds there is someone to answer to.
Annie Woods is someone that Hunter is in love with. As an analyst with the CIA she is able to learn a lot of her fellow citizens and one person she is very interested in, as the series begins, is who the vigilante exacting justice really is. She does not know her target is her love. He does not know that his love is after him.
Back on Hunter, if you were to look deeply into his history, officially, you would only go back about three years. Before that, nothing. And a lot of people throughout the series try very hard to go deeper and some of those folks have a lot of money and influence so if anyone could break the secrecy, they could. And they can't.
We the readers learn early on that the past of Hunter, which is obviously not his real name, involves a fair number of years being a very skilled and capable operative with the Agency. And then for reason you can learn for yourself, he quit and created the identify of Hunter and started life anew. We also discover that he had help in doing so from an old friend at the Agency and with a lot of experience living under fake identities. That and the fact that his deceased parents had been very well off and had left him their fortune. Having the kind of money we are talking about helps in all sorts of ways.
So we see that Hunter is a reporter. He is also a vigilante. And he is an enigma with no past to a lot of people. He is also a lot of fun watching him do what he does.