Deveraux, codename the November Man, is an agent for the CIA.
This highly experience agent whose first name is never revealed, works for R Section of the CIA Under a man named Hanley, referred to as an "asshole" by Deveraux in the second page of the first book and expanded upon throughout the series.
He is extremely good at his job, which makes him valuable, but he doesn't suffer well the fools and incompetents above him, which makes him undesirable. It makes the series delicious. Also making the series something to read are two recurring characters.
The first is Rita, the reporter that Deveraux meets, fights with, falls in love with, leaves, reunites, and everything in between. She is beautiful, gutsy, individualistic, and worth Deveraux coming home to, even if some times he doesn't know it.
The other is Henry McGee, one of the greatest villians ever created for a spy series. First off, that may or may not be who he is. Did he kill the real McGee or just make it look like he did. Secondly, just as Bond had his Blofeld, a criminal mastermind with a large organization behind him, Deveraux has McGee. No organization and no criminal mastermind, he is nevertheless a genius when it comes to causing trouble and when you know he's looking to hurt someone you love, you start sweating. Like all good archnemesies, he is not in all the books or even in most of them but when he is around, he is scary.
Which makes the character of Deveraux so much the better. He has a hard time stopping McGee but that just shows he is human (and written that way, too) but he stays the course and has the decency to want revenge on the man.