Maurice Le Noblet Duplessis (French pronunciation: ​[dyplɛsi]; April 20, 1890 – September 7, 1959), byname "Le Chef" ("The Boss"), was a Canadian lawyer and politician who served as the 16th premier of Quebec. A conservative, nationalist, populist, anti-communist, anti-unionist and fervent Catholic, Duplessis and his party, the Union Nationale, dominated provincial politics from the 1930s to the 1950s. He is the longest-serving premier of Quebec since Confederation by cumulative time of service, having led the province for 18 years.

Son of Nérée Duplessis, a lawyer who served as a Conservative member of the Legislative Assembly (MLA), Maurice studied law in Montreal and became a member of the Bar of Quebec in 1913. He then returned to his home town of Trois-Rivières to practice law, where he founded a successful consultancy. Duplessis narrowly lost the campaign for the Trois-Rivières seat in the 1923 election, but managed to get elected in 1927 as a Conservative MLA. His rhetorical skills helped him become the leader of the Official Opposition in the Legislative Assembly in 1933 in the place of Camillien Houde. As opposition leader, he agreed to a coalition with Paul Gouin's Action libérale nationale (ALN), which they called the Union Nationale. It lost in 1935 but gained a majority the following year as Gouin retired from politics and Duplessis took over the leadership, thus breaking almost 40 years of uninterrupted rule by the Quebec Liberal Party. Le Chef, in addition to his premiership duties, assigned himself the role of Attorney General and briefly held other ministerial posts as well.

The first three years in government were difficult for Duplessis as the government struggled to respond to the ongoing hardships of the Great Depression. That term saw the introduction of several key welfare policies (such as the universal minimum wage and old-age pensions), but the effort to strengthen his rule by calling a snap election in 1939 failed as his campaigning on the issue of World War II backfired and his government left the economy in a poor state. However, the Conscription Crisis of 1944 propelled him back to power in that year's election, which Le Chef would exercise until his death. As was the general trend of the time, he presided over a period of robust economic growth due to the rising demand in resources, which the province used to develop Côte-Nord and rural areas. Duplessis was a strong proponent of economic liberalism and implemented pro-business policies by keeping taxes low, refraining from regulation and adopting pro-employer labour policies, in particular by cracking down on trade unions. Le Chef usually met the federal government's initiatives with strong resistance due to his convictions on provincial autonomy. In the social domain, Duplessis maintained and protected the traditional role of the Catholic Church in Quebec's society, notably in healthcare and education. Le Chef was ruthless to the perceived enemies of the Church or of the Catholic nature of the province, such as Jehovah's Witnesses. Communists were persecuted under the Padlock Law, which he authored in 1937.

Duplessis's legacy remains controversial more than 60 years after his death. Compared to the Anglophones, the French Canadians remained worse off in the province where they constituted a majority just as his government was courting Anglophone and out-of-province businessmen to invest. This clientelist relationship with the business spheres often morphed into outright corruption. Le Chef's authoritarian inclinations, his all-powerful electoral machine, staunch conservatism, a cozy relationship with the Catholic Church, the mistreatment of Duplessis Orphans and the apparent backwardness of his model of development were also subject of criticism. Thus his critics labelled the period the Grande Noirceur (Great Darkness), which stuck in Quebec's society in a large degree thanks to the efforts of those who led the Quiet Revolution in the 1960s. This was also the initial general opinion of historians and intellectuals, but since the 1990s, academics have revisited Duplessism and concluded that this assessment required nuancing and placement in the contemporary perspective and, in some cases, advocated outright rejection of that label.