At the beginning of Spectre James Bond first meets Max Denbigh, the head of the new Joint Security Service that's supposed to merge MI5 and MI6 into one. He choses to call him "C", though:
Bond: Congratulations on your new appointment...I suppose we should call you C now.
Denbigh: No, no. "Max," please.
Bond: No, I think I'll call you C, C.
Denbigh: As you wish.
This is also the name with which Andrew Scott's character is credited and in line with the tradtion of single-letter designations as known from M and Q (and the real British secret services). But why is he called by that letter and why does James put so much emphasis on it? Now it could as well just be a name without much significance and simply the nickname Denbigh bears in the Joint Security Service, but it seemed like Bond decided to call him that way out of the blue and as if he had a specific reason to choose the letter C. So did Bond actually choose that name personally for him or is that really Max Denbigh's official designation. In any case, why? Is there anything more to the letter C as Max Denbigh's designation other than sheer randomness? And why did James Bond put so much emphasis onto it in that scene?
It was hinted in previous installments that M actually seems to relate to Judi Dench's character's real name (as well as to Gareth Mallory's). Likewise was C actually the sign of the real MI6's first head (as also based on his last name), who seemed to have started that tradition. Yet there doesn't seem to be any relation between Max Denbigh and the letter C.