Stephen Dain is a troubleshooter for Military Intelligence.
Exactly which branch he works regularly it not revealed. When asked by a friend in the FBI if he was still working out of the State Department, Dain responded that he was working for the Treasury, to which his friend said it was hard to keep up. What this, and other evidence, points to is that Dain is known in the Intelligence community as the man to call when no one else can do the job, or wants to be known to have done it. As further evidence of this, in a subsequent adventure Dain is in the Middle East working on a case for Military Intelligence when another case came to his attention, this time involving white slavery. Dain had to complete his previous mission before he could get away and it was likely the State Department that sanctioned his actions. In the last book in the series his temporary employer seems to be international in nature though the work remains the same.
A 6' tall, thin, sinewy man in his late 30's, he is both nondescript in a crowd and daunting up close. He "hid his virtues for the sake of expediency and concealed his vices out of respect for his vanity." He is also reported to be polite, reserved, and self-contained. One man who met him thought that he would not want to be an enemy of Dain and that even a friend might have to be careful.
He has been an agent for enough time to be jaded about virtually every cause. As mentioned in one book, "he did his work well but he did very little else. He was more useful to others than to himself." In another instance while discussing police and criminals the world over, he commented that often policemen and crooks were very similar and "it may be a case of symbiosis. Or perhaps some men are just naturally drawn to crime. Then it becomes an unimportant matter of pure accident which aspect of it they work in."
The novels about Dain vary considerably. Dain is never the main focus of any of the books. He is, rather, a man who steps in when he is needed and then steps back to let others do their job. He is always in command but seldom takes the role of leader. In each case there comes a time that Dain feels his work is over and he leaves, sometimes with a fair amount of the book left in which the mopping up occurs.