A giant of Canadian history. A hapless bachelor who practically worshipped his mother. A racist and antisemite typical of his generation. A devoted occultist. An astoundingly effective Liberal Party leader. The Enduring Riddle of Mackenzie King explores the character, thoughts, and actions of Canada’s longest-serving prime minister. In his lifetime, Canadians often dismissed William Lyon Mackenzie King as a meritless interloper, yet numerous scholars have since ranked him as the best prime minister ever. Patrice Dutil leads a who’s who of historians to discuss why King deserves that estimation – or why not. Many particularly admire King’s management of the Canadian war effort. At the same time, he has been condemned for racist immigration policies, the incarceration of Japanese-Canadians, and his indifference toward Indigenous peoples. King often headed minority governments and was sometimes personally defeated in elections. Yet his political accomplishments are unmatched: he presided over the nation during the expansionist 1920s and part of the Depression, kept Canada whole during the Second World War, and established the welfare state. This fresh, full assessment forms a new take on how King may – or may not – be the greatest of all Canadian prime ministers.