Sven Olof Joachim Palme (/ˈpɑːlmə/; Swedish: [ˈûːlɔf ˈpâlːmɛ] ^ⓘ; 30 January 1927 – 28 February 1986) was a Swedish politician and statesman who served as Prime Minister of Sweden from 1969 to 1976 and 1982 to 1986. Palme led the Swedish Social Democratic Party from 1969 until his assassination in 1986.

A longtime protégé of Prime Minister Tage Erlander, he became Prime Minister of Sweden and Chairman of the Social Democratic Party in 1969. He left office after failing to form a government after the 1976 general election, which ended 40 years of unbroken rule by the Social Democratic Party. While he served as a Leader of the Opposition, he also served as special mediator of the United Nations in the Iran–Iraq War, and was President of the Nordic Council in 1979. He faced a second defeat in 1979, but he returned as prime minister after electoral victories in 1982 and 1985, and served until his death.

Palme was a pivotal and polarizing figure domestically as well as in international politics from the 1960s onward. He was steadfast in his non-alignment policy towards the superpowers, accompanied by support for numerous liberation movements following decolonization including, most controversially, economic and vocal support for a number of Third World governments. He was the first Western head of government to visit Cuba after its revolution, giving a speech in Santiago praising contemporary Cuban revolutionaries.

Frequently a critic of Soviet and American foreign policy, he expressed his resistance to imperialist ambitions and authoritarian regimes, including those of Francisco Franco of Spain, Augusto Pinochet of Chile, Leonid Brezhnev of the Soviet Union, António de Oliveira Salazar of Portugal, Gustáv Husák of Czechoslovakia, and most notably John Vorster and P. W. Botha of South Africa, denouncing apartheid as a "particularly gruesome system". His 1972 condemnation of American bombings in Hanoi, comparing the bombings to a number of historical crimes including the bombing of Guernica, the massacres of Oradour-sur-glane, Babi Yar, Katyn, Lidice and Sharpeville and the extermination of Jews and other groups at Treblinka, resulted in a temporary freeze in Sweden–United States relations.

Palme's assassination on a Stockholm street on 28 February 1986 was the first murder of a national leader in Sweden since Gustav III in 1792, and had a great impact across Scandinavia. Local convict and addict Christer Pettersson was originally convicted of the murder in Stockholm District Court but was unanimously acquitted by the Svea Court of Appeal.

On 10 June 2020, Swedish prosecutors held a press conference to announce that there was "reasonable evidence" that Stig Engström had killed Palme. As Engström had killed himself in 2000, the authorities announced that the investigation into Palme's death was to be closed. The 2020 conclusion has faced widespread criticism from lawyers, police officers and journalists, decrying the evidence as only circumstantial, and – by the prosecutors' own admission – too weak to ensure a trial had the suspect been alive. The true identity of his assassin remains unknown.

Sven Olof Joachim Palme was born on 30 January 1927 into an upper class, conservative Lutheran family in the Östermalm district of Stockholm. The progenitor of the Palme family was skipper Palme Lydert of Ystad of either Dutch or German ancestry. His sons adopted the surname Palme. Many of the early Palmes were vicars and judges in Scania. One branch of the family, of which Olof Palme was part, and which became more affluent, relocated to Kalmar; that branch is related to several other prominent Swedish families such as the Kreugers, von Sydows and the Wallenbergs. His father, Gunnar Palme [sv] (1886–1934), was a businessman, son of Sven Theodore Palme [sv] (1854–1934) and Swedish-speaking Finnish Baroness Hanna Maria von Born-Sarvilahti [fi] (1861–1959). Through her, Olof Palme claimed ancestry from King Johan III of Sweden, his father King Gustav Vasa of Sweden and King Frederick I of Denmark and Norway. His mother, Elisabeth von Knieriem (1890–1972), of the Knieriem family who originated from Quedlinburg, descended from Baltic German burghers and clergy and had arrived in Sweden from Russia as a refugee in 1915. Elisabeth's great-great-great grandfather Johann Melchior von Knieriem (1758–1817) had been ennobled by the Emperor Alexander I of Russia in 1814. The von Knieriem family does not count as members of any of the Baltic knighthoods.^{[citation needed]} Palme's father died when he was seven years old. Despite his background, his political orientation came to be influenced by Social Democratic attitudes. His travels in the Third World, as well as the United States, where he saw deep economic inequality and racial segregation, helped to develop these views.

A sickly child, Olof Palme received his education from private tutors. Even as a child he gained knowledge of two foreign languages — German and English. He studied at Sigtunaskolan Humanistiska Läroverket, one of Sweden's few residential high schools, and passed the university entrance examination with high marks at the age of 17. He was called up into the Army in January 1945 and did his compulsory military service at Svea Artillery Regiment between 1945 and 1947, becoming in 1956 a reserve officer with the rank of Captain in the Artillery. After he was discharged from military service in March 1947, he enrolled at Stockholm University.^{[unreliable source?]}