MI6 Hires M

M in the James Bond movie franchise was only female 1/7 times - (the inimitable) Dame Judi Dench https://en.wikipedia.org/wiki/Judi_Dench. Other's who played the part - Bernard Lee https://en.wikipedia.org/wiki/Bernard_Lee, Robert Brown https://en.wikipedia.org/wiki/Robert_Brown_(British_actor), Ralph Fiennes https://en.wikipedia.org/wiki/Ralph_Fiennes, John Huston https://en.wikipedia.org/wiki/John_Huston, David Niven https://en.wikipedia.org/wiki/David_Niven, Edward Fox https://en.wikipedia.org/wiki/Edward_Fox_(actor).

In the books M was M.M., his first name being Miles.