John Brock is an agent for a secret British Intelligence agency.
He has been one for almost a decade and a half, since the end of WWII when he was first noticed by the Fat Man. Brock had been drinking and carousing and getting into fights as worked as hard as he could to blow the little money given upon his discharge from the military. The Fat Man, as Brock always thought of him, watched how well he handled himself and how little he cared for fighting fair, only winning, and decided he could use a man like Brock in his organization. So he paid for more drinking, night after night, and watched over and over how Brock would get out of trouble he got himself into.
Then when Brock was dead broke and banned from every bar in the Brighton area, the Fat Man offered him a job. Brock told him to get stuffed and left. He headed to London to try to get a job in advertising but the Fat Man soon sent two associates to bring him him and he reluctantly went. It was also reluctantly that he stayed in the secret facility for the next three months learning how to do a lot of things that normal citizens had no reason to know ranging from the kiss of life to the kiss of death.
At that point, the Fat Man gave Brock his first assignment and, because he "was young and keen and stupid", he did it. It proved to be totally unnecessary, totally illegal, and all fully documented by the Fat Man. From that day on, if asked to do a job, Brock knew that refusal meant evidence being released that would get him sent "to Germany to be electrocuted, then brought back ... to be hung." In fact, Brock realized that he had broken more laws than he had known existed and he belonged to the Fat Man. But the Fat Man didn't want him all the time so he was free to go about his planned business.
And so for the past many years, Brock has worked in a very easy job in advertising where day after day he dealt with fools at the top giving orders to "zombies" to give to workers like him to do and he would drink a lot and and chase a lot of women. But one or twice each year, he will be invited to the headquarters in Kensington Gardens and off he would go to some different place and do things that he shouldn't do, all for the sake of his country and only when the Fat Man demands.