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William Lyon Mackenzie King (December 17, 1874 – July 22, 1950) was the prime minister of Canada for three non-consecutive terms from 1921 to 1926, 1926 to 1930, and 1935 to 1948. A Liberal, he was the dominant politician in Canada from the early 1920s to the late 1940s. With a total of 21 years and 154 days in office, he remains the longest-serving prime minister in Canadian history.
King studied law and political economy in the 1890s and later obtained a PhD, the first Canadian prime minister to have done so. In 1900, he became deputy minister of the Canadian government's new Department of Labour. He entered the House of Commons in 1908 before becoming the first federal minister of labour in 1909 under Prime Minister Wilfrid Laurier. After losing his seat in the 1911 federal election, King worked for the Rockefeller Foundation before briefly working as an industrial consultant. Following the death of Laurier in 1919, King won to the leadership of the Liberal Party. Taking the helm of a party torn apart by the Conscription Crisis of 1917, he unified both the pro-conscription and anti-conscription factions of the party, leading it to victory in the 1921 federal election.