Fox Elton is an agent with U.S. Army Intelligence.
The activities of this interesting operative take place in the final days of world War I. While no specific dates are given to pinpoint the time, statements made show that Elton has been on duty for enough time to have earned a very good reputation at his job and since America entered the Great War in April, 1917, tacking on at least six months would place events in late 1917 or early 1918.
He holds the rank of Captain in that organization when we first meet him; said group referred initially as the Army Intelligence Service (AIS).
Our introduction to him takes place as he attends a meeting between the head of the French espionage system and the AIS chief, and Elton's boss, Colonel Rand. Elton is sitting with his "clear blue eyes with serenely calm features" as he listens to Rand rail at his opposite because that man is insisting a major German spymaster, recently put to the guillotine, was still operating a spy nest in Paris. "How do you get him back on earth after chopping off his head?" poses Rand.
Elton's presence turns out fortuitous as a code received by the French from that dead spy is shown and handed by Rand to Elton with a "you are the code expert of our official family". As we will see often in the adventures of Elton to come, he is indeed a whiz at breaking codes, often taking just a short time to do so. Decrypting cyphers is not only something Elton is more than qualified in, it is an obvious passion for him and he relishes in not only breaking a coded message but also explaining to anyone close to him (and therefore we readers) exactly how the code works and why.
Elton came to Army Intelligence on a loan from his previous employer, the Department of Justice, where he had been an operative for some time. This tacks on a tad bit of confusion as to how old Elton in for in his recorded escapades it comes across that he is still fairly young (certainly his boss Rand considers him as such) but tossing in his prior experience with the DOJ and the exact age is in question. I would place it as around the late 20s since it is near certain he graduated college, followed by the DOJ stint and now a year or so of war service during WWI.
What Elton has in the way of an outside life is never discussed; he is in the thick of fighting the Germans and has no time for anything else.