Robert Harmon is a professor at Columbia.
That is, he is when he is not being mistaken for a spy and being forced to act like one. Though in truth he once was a spy, but that was thirty years before in the OSS during WWII. He left all that behind decades before to become a well-respected teacher at a prestigious university. Spying was something in his distant past.
Back during the War, he had worked behind enemy lines in numerous countries, taking on a variety of missions including eliminating key military personnel. He was fairly good at it but, as he admits, he was a lot younger and in much better shape. Those days were long gone.
As the series begins, Harmon is a professor well into his 50s, teaching the History of Ideas at the prestigious New York university. He is happily single and planning on staying that way. He is enjoying the chance to get away on vacation with a sexy graduate student of his - not something his dean would approve of but something he is quite enjoying. It is not all play, though, as he was tasked with reviewing evidence which a colleague claimed proved that many professors, like himself, were really being paid by the CIA. Harmon is certain it is nonsence.
Certainly for him the thought of returning to his days as an undercover operative is nowhere around. Those days are through. But sometimes everything old is new again and Harmon finds himself, in the first novel, forced to remember old habits to stay alive. And then in the second, still not as happy about things as he could be, he is pressed into action again.
Luckily, Harmon manages to keep his sense of humor when all others cannot find theirs.