Judi Dench is my favorite M.
Her first scene tho
Bill Tanner: Seems your hunch was right, 007. It’s too bad the Evil Queen of Numbers wouldn’t let you play it… [M appears behind him, everyone makes the “oh shit stop talking right now” face, Tanner winces]
M: You were saying?
Bill Tanner: No, no, I was just… just um…
M: Good. Because if I want sarcasm, Mr Tanner, I’ll talk to my children, thank you very much.