Not surprisingly, neither of these are his real name. Julie always refers to him as the "Bloody Machiavellian English Intelligence Officer playing God" in a reference to Niccolò Machiavelli, author of the political treatise The Prince, in which the author basically advocates a whole lot of ideas that essentially say "do what you have to to get what you want." He's the one who gets Julie and then Maddie involved in SOE activities.
When he debriefs Maddie, she gives him the nickname John Balliol, "a good ironic name, the miserable Scottish king William Wallace lost his life defending" (2.26.2), implying that he hides behind braver people. His sympathy with von Linden's suicide and his impotent grief for Julie indicate that he and von Linden are really two sides of the same coin.