Mike Manly is an agent with American Intelligence.
That is about as close to identifying who he works for as I can. In the three recorded adventures we have of this operative, we know from the first that he is a "Secret Agent ... from Washington", from the second we find him at FBI headquarters though no one actually says he works there, and from the third we see him getting his orders from a bossy older fellow manning a desk at "Washington DC, Headquarters of the Secret Service" but again nothing stating he worked for that agency.
Manly is certainly an experienced agent because he is sent on these highly dangerous and important missions by himself, showing his bosses have confidence in his skills. Since he successfully completes all of them quickly and succinctly, that attitude is warranted.
We also know from the silver streaks in his black hair that he is not a young man just out of training. He is self-assured and daring as displayed by the fact that he, on the third mission, does not hesitate to climb the Eiffel Tower to get at his quarry. We also see in that same assignment that he is cool with the ladies for when a sexy femme fatale makes a play for him, he is suave and smooth with her while keeping an eye out for attackers.
He is also stylish in dress. While wearing the requisite suit for the times, instead of a traditionally dark colored tie, we find him with a light green one in one mission, a red one in another, and a yellow one in the last. All of these with a blue suit jacket.
He takes his work very seriously, which is good since lots of people are trying to kill him. Though he was talking about another agent, he could just as easily be referencing himself when he refers to agents like them as "the kind of soldier that is fighting the silent war that is keeping the Cold War from turning hot!"