1. M - For Your Eyes Only
M is such a quintessential part of the James Bond world that when the Daniel Craig version of the character rebooted the continuity, the head of MI6 managed to survive the grittifying of the spy genre, unlike other stalwarts Q and Moneypenny. This doesn't, however, mean that M has appeared in every Bond film. Over two decades Bernard Lee had weathered three Bonds, but after eleven films he died, just before he could shoot his scenes for For Your Eyes Only. Out respect for the actor the role wasn't hurriedly recast, instead Bill Tanner took on the role of giving Bond his mission while M was 'on leave'. Robert Brown took the role for Octopussy and continued until the franchise stagnated under Timothy Dalton. Whats interesting about M is that, unlike Bond himself, the different actors are meant to be playing different characters in the same job. This is most touchingly seen in The World Is Not Enough, where a painting of Lee can be seen at MI6s Scottish headquarters (and more obviously through the entire plot of Skyfall).
Any more characters who inexplicably missed only one entry? Wish any of these (hint hint Alan Grant) had stayed away from the franchise)? Let us know in the comments below.