Who was William Lyon Mackenzie King?

William Lyon Mackenzie King (December 17, 1874 to July 22, 1950) was the longest-serving Prime Minister of Canada, with about 21 years and 5 months in office over three non-consecutive terms (December 29, 1921 to June 28, 1926; September 25, 1926 to August 7, 1930; October 23, 1935 to November 15, 1948). King was a Liberal and led the Liberal Party of Canada from 1919 to 1948.

King was born in Berlin, Ontario (renamed Kitchener in 1916) and was the grandson of William Lyon Mackenzie, the 1837 Upper Canada Rebellion leader. He earned a doctorate from Harvard University and worked as a labour-relations consultant for the Rockefeller Foundation before entering politics. As Liberal leader from 1919 he won the federal election of December 6, 1921 (Canada's first three-party election, with the Progressive Party winning 65 seats but declining to form Official Opposition). King's first government established the Canada Pension Plan precursor (the Old Age Pensions Act of 1927).

King's government navigated the King-Byng Affair of June to September 1926, a constitutional crisis in which Governor General Lord Byng refused King's request for dissolution of Parliament after King lost a confidence vote. The affair (Canada's only serious test of the reserve powers in modern history) led to the 1926 Imperial Conference declaring the equality of Britain and the Dominions, and ultimately to the Statute of Westminster of 1931 confirming Dominion sovereignty.

King's longest tenure (1935 to 1948) covered the latter half of the Great Depression and the Second World War. King introduced the Canada-United States free-trade Reciprocity Agreement of 1935, the federal Unemployment Insurance Act of 1940, the federal Family Allowance Act of 1944 (Canada's first universal social-welfare programme), the Industrial Disputes Investigation Act, and the federal income-tax structure that funded the expanded postwar state. King led Canada through the Second World War, with about 1.1 million Canadians serving and about 45,000 deaths. King handled the 1942 Conscription Plebiscite carefully (his famous phrase 'Not necessarily conscription, but conscription if necessary') and avoided splitting the country. King retired in 1948 and died in 1950 at his estate Kingsmere in the Gatineau Hills.