John Benham is an agent with MI5.
When we meet him in the first recorded adventure, the year is 1945 and the European theater of the Second World War was a half dozen weeks away. At that time, he was deeply involved in activity often deep inside enemy territory so at the time his bosses were more accurately just referred to as Military Intelligence but later when the demarkation between MI5 and MI6 became more defined, he would remain with the former.
Benham holds the rank of Captain in our initial meet but he will get promoted to Major before the second adventure. His advance will be very much merited for as he tells us with no bragging but some pride, he had already been sent into German-occupied France one more than one occasion, parachuting in under orders to help set up affairs before D-Day. His missions came to him since he was seconded to intelligence work from his normal duties "in a certain County Regiment".
We are told that Benham was a good choice for such clandestine work because, thanks to his family's origins in Switzerland and his still having relatives there he visited often before the War, "my German [was] as good as my English and my French not far behind". Add to that what he considers his appearance is "nothing much to look at" with him describing himself as a "plain, blunt man". This average look made him easy to blend in and easy to forget and with his command of the languages and his "knowledge of the mentality of the average German", he was able to pass as either a Frenchman or a German whenever the need arose.
Benham is, on that first meeting, 36 years of age and apparently still single, not surprising with the War going on. He has just undergone a period of recuperation from severe injuries suffered during his last mission to Caen but he is healed sufficient to be ready for duty again and even more anxious to be back at it.