Remsen is an agent with the CIA.
The three-book series about the graying, experienced operative Remsen and those with whom he has contact, are referred to as "Spy Thriller of Romantic Suspense". In each of the adventures, young beautiful women are placed into terrifying and highly dangerous situations, surrounded by agents who feel the mission is far more important than the few that might get hurt.
In each book the different women will meet and fall in love with handsome spies who work for Remsen, thus fulfilling the romantic suspense part. In each book the agents engage in exciting espionage activity, taking care of the spy thriller. It is of note that the two do not contradict each other - the adventures work.
About Remsen very little is ever said, including what his first name is, assuming that Remsen is not the first name. He is by no means a young man anymore, having worked in the spy game since WWII and possibly before, making him at least in his mid 40's. Based on the descriptions and his attitudes, he is probably older. He holds a position of some power and respect and at one point is almost certainly Chief of Station in one European country.
Remsen is devoted to getting the job done. He by no means wants injury or worse to befall the ladies who get involved in the cases and he does go out of his way to make as sure as he can that they remain unharmed but the mission is the biggest priority. He is still a romantic at heart, though, and takes some pleasure in seeing the women meeting men he feels will treat them properly.