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Olivia Mansfield, better known as M, was the head of the British Secret Service, MI6. She is well-established in her role; remarking at one point "Christ, I miss the Cold War." Mansfield was eventually killed by rogue agent Raoul Silva, becoming the first M to die in the line of duty, and was succeeded by Gareth Mallory.
Mansfield appeared in Casino Royale, Quantum of Solace and Skyfall, portrayed by Dame Judi Dench, who had previously played Barbara Mawdsley during the Brosnan era. Dench reprised the role in an uncredited cameo in Spectre.