Thomas Buchanan is an agent for the President.
Officially, when we first meet him, he is a Special Agent for the FBI, putting the final sentences to the typewritten report on a concluding securities case. He is 32 years old, a man considered by most to be quite handsome with sandy colored hair and in good physical shape as would be expected by any of Hoover's field agents, though nothing . Later he would employed by the still fairly new, and considered archrival of the FBI, the CIA as one of their operatives.
But as the name of the two initial adventures we have of Buchanan, he will find his most challenging work when he is asked by two succeeding Chief Executives to handle things for them, mostly on the downlow.
The year we first encounter Buchanan is 1949. He is finishing up his third year with the Bureau having joined shortly after being released from service as an infantry captain in the Army during WWII. Having an Italian immigrant mother gave him a fluency in that language so when his unit was part of the campaign to invade Sicily and then Italy, his skills there were of great use. After the War, though, listlessness was a problem that was solved by giving federal law enforcement a chance.
Buchanan is honest enough with himself to know that while he found the work at the Bureau interesting, he was by no means a company man, and certainly not a Hoover man as he found the FBI top man to be less than worthy of the adoration he got from some sources and more than a lot deserving the condemnation coming from other quarters. He is in the process of reevaluating his role with the Bureau when his name comes to the attention of the nation's Chief Executive.
The not-so-petty squabbles between the firmly established FBI and the nascent and thought upstart CIA was increasing as the head of the former wanted the latter done away with and the head of the latter had few good thoughts about the other. In the middle is Truman who would love to see Hoover knocked down a few pegs if not booted out completely. To accomplish that, he needed a good tool.
Buchanan, not knowing it at the time, was to be that tool.