Maxim Gunn is an agent for the Organization.
The Organization, for this highly secret member of the British Intelligence community has no official title, has a nearly unlimited budget and is answerable only to the Prime Minister. Its mission is to take care of those problems that are beyond the scope or capability of the other agencies. Considering the witchcraft, demonology, monsters, and such that Gunn has to fight, it's understandable how traditional teams might not be qualified. Gunn, however, faces them all with panache, as though outré is normal. While he might not believe everything he sees at first glance, he seldom seems overly ruffled no matter how bizarre.
Gunn appears to be a modernized version of James Bond in that he is dashing, debonair, sophisticated, and is used to and much enjoys the finer aspects of life, including driving a Lamborhini to all the right clubs. Instead of a Walther PPK, however, Gun prefers the stopping power of a .357 Magnum. Considering the nature of the enemies he has to face, it is a good thing he carries such fire power.
As the series opens, Gunn has been an agent for a considerable number of years and is truly believing that the law of averages was catching up. Knowing it was just a matter of time before Lady Luck didn't favor him, he felt quitting was in order. When thrown in is the mutual dislike he and his boss feel and the desire for a "normal" life, his discontent is strong.
But there always is one more catastrophe to take care of.