William Lyon Mackenzie King was a Canadian statesman and politician who was the tenth 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. King is best known for his leadership of Canada throughout the Great Depression and the Second World War. He played a major role in laying the foundations of the Canadian welfare state and established Canada's international reputation as a middle power fully committed to world order. With a total of 21 years and 154 days in office, he remains the longest-serving prime minister in Canadian history.

The King's Privy Council for Canada, sometimes called His Majesty's Privy Council for Canada or simply the Privy Council (PC), is the full group of personal consultants to the monarch of Canada on state and constitutional affairs. Practically, the tenets of responsible government require the sovereign or his viceroy, the governor general of Canada, to almost always follow only that advice tendered by the Cabinet: a committee within the Privy Council composed usually of elected members of Parliament. Those summoned to the KPC are appointed for life by the governor general on the advice of the prime minister of Canada, meaning that the group is composed predominantly of former Cabinet ministers, with some others having been inducted as an honorary gesture. Those in the council are accorded the use of an honorific style and post-nominal letters, as well as various signifiers of precedence.