Karl Hjalmar Branting was a Swedish politician who was the leader of the Swedish Social Democratic Party (SAP) from 1907 until his death in 1925, and three times Prime Minister of Sweden. When Branting came to power in 1920, he was the first Social Democratic Prime Minister of Sweden. When taking office for a second term after the general election of 1921, he became the first democratic socialist head of government in Western Europe elected under universal suffrage. An early supporter of modern social democracy and democratic socialism, he led the SAP through a transformation from a radical socialist movement to Sweden's dominant party; the Social Democrats have been Sweden's largest party in every election since 1914, and formed government for 44 continuous years from 1932 to 1976.

The Swedish Social Democratic Party, formally the Swedish Social Democratic Workers' Party, usually referred to as The Social Democrats, is a centre-left social-democratic and democratic socialist political party in Sweden. Globally, it is a full member of the Progressive Alliance and the Party of European Socialists.