Captain Maddox is a member of the British S.O.E.
That acronym stands for the Special Operations Executive, whose "purpose was to conduct espionage, sabotage and reconnaissance in occupied Europe (and later, also in occupied Southeast Asia) against the Axis powers, and to aid local resistance movements." The exploits of the members of this organization, where not kept classified, have been extremely impressive and that holds true with Maddox.
Maddox, when we first meet him is an experienced agent. The S.O.E. was created in 1940 and one of its first operatives was Maddox. Since the recorded adventures we have of Maddox start in 1944, he has been around for several quite active years. Moreover, he has one very impressive record showing clearly that the man is quite good at getting the job done. As the job invariably for him means operating in dangerous conditions with little or no backup, Maddox has shown to be a force. He has earned a DSO as well as a DSC for his accomplishments and his name is known to Churchill for his actions.
He has also shown that he does not play the political game at all. As his immediately supervisor growls at him, "Maddox, you're thirty-two-years-old and you've a natural talent for soldiering. By your age, with your experience, you should have my rank [Brigadier]. But your insubordination, your penchant for not going through the proper chain of command, your propensity for disobeying orders..." When Maddox points out that he had never actually disobeyed any direct order, the man countered, "Yes, but you're not exactly renowned for following them, either". In addition to his doing things his own way, Maddox is known for his blunt honesty. He is not rude by any means but he does have a refreshing habit of cutting through malarkey to get at the importance of a matter.
Maddox is a widower. His wife died in an air raid the year before we meet him leaving him with a young son. He has the much appreciated help of his in-laws to tend for the child especially when he is forced to leave on assignments fairly often and be gone for weeks each time.
One other important fact on Maddox that is unpleasant to say but is even more unpleasant for him to have to endure. Shortly after his wife died, Maddox was sent on a mission to Burma and there while in a foxhole awaiting a Japanese squad to ambush, he contracted "bilharzia", aka 'snail fever', "the second-most devastating disease in the world, after malaria". "The burrowing little worms were transmitted by snails so tiny you could barely see them as you waded through muddy waters in Libya or Siam or Ghana." Quite disturbing.