Paul Knox is an agent with the World Circle Agency.
That fairly impressive name for an intelligence organization is, to some, just a glorified international private investigative company, peeking in keyholes in more than one country. To those with a bit more global outlook, it is a private intelligence gathering corporation "more than one government used as its espionage arm or as an adjunct to it, depending on the size and wealth of the government".
This would include on many occasions the American government and when that is the case we learn that "on jobs that might be concerned with the security of the United States - directly or indirectly - Knox usually carried the blessings of the Government". That helps when Knox finds himself in a sticky situation which seems fairly common.
Knox is an agent with the firm because he loves the action and the excitement. It was the same reason he had chosen years before to become a police officer and later a detective. He was especially good at the last one and had racked up an impressive number of cases before he got an offer to expand his beat and left the guys in blue to become a guy in a trenchcoat.
Money was certainly not the reason he became either a cop or an agent. He had quite a bit of his own, thanks to inheritances from his uncle and his father, both of whom were very well off and who left Knox their bounty when they passed. When he was a cop, Knox made sure his wealth was not made an issue by always wearing the same sort of clothes his fellow officers wore and went the same bars and clubs they did and never flashed his money in their faces, something they respected and appreciated. Now that he moves in different circles, though, he feels more freedom to go a bit more splashy.
No matter what kind of footwear Knox might sport nowadays, he is still a gumshoe and he still loves it.