Salvador Guillermo Allende Gossens (26 June 1908 – 11 September 1973) was a Chilean socialist politician who served as the 28th president of Chile from 1970 until his death in 1973. As a socialist committed to democracy, he has been described as the first Marxist to be elected president in a liberal democracy in Latin America.

Allende's involvement in Chilean politics spanned a period of nearly forty years, during which he held various positions including senator, deputy, and cabinet minister. As a life-long committed member of the Socialist Party of Chile, whose foundation he had actively contributed to, he unsuccessfully ran for the national presidency in the 1952, 1958, and 1964 elections. In 1970, he won the presidency as the candidate of the Popular Unity coalition in a close three-way race. He was elected in a run-off by Congress, as no candidate had gained a majority. In office, Allende pursued a policy he called "The Chilean Path to Socialism". The coalition government was far from unanimous. Allende said that he was committed to democracy and represented the more moderate faction of the Socialist Party, while the radical wing sought a more radical course. Instead, the Communist Party of Chile favored a gradual and cautious approach that sought cooperation with Christian democrats, which proved influential for the Italian Communist Party and the Historic Compromise.

As president, Allende sought to nationalize major industries, expand education, and improve the living standards of the working class. He clashed with the right-wing parties that controlled Congress and with the judiciary. On 11 September 1973, the military moved to oust Allende in a coup d'état supported by the CIA, which initially denied the allegations. In 2000, the CIA admitted its role in the 1970 kidnapping of General René Schneider who had refused to use the army to stop Allende's inauguration. Declassified documents released in 2023 showed that US president Richard Nixon, his national security advisor Henry Kissinger, and the United States government, which had branded Allende as a "dangerous" communist, were aware of the military's plans to overthrow Allende's democratically elected government in the days before the coup d'état. As troops surrounded La Moneda Palace, Allende gave his last speech vowing not to resign. Later that day, Allende died by suicide in his office; the exact circumstances of his death are still disputed.

Following Allende's death, General Augusto Pinochet refused to return authority to a civilian government, and Chile was later ruled by the Government Junta, ending more than four decades of uninterrupted democratic governance, a period known as the Presidential Republic. The military junta that took over dissolved Congress, suspended the Constitution of 1925, and initiated a program of persecuting alleged dissidents, in which at least 3,095 civilians disappeared or were killed. Pinochet's military dictatorship only ended after the successful internationally backed 1989 constitutional referendum led to the peaceful Chilean transition to democracy.

Allende was born on 26 June 1908 in Santiago. He was the son of Salvador Allende Castro and Laura Gossens Uribe. Allende's family belonged to the Chilean upper middle class and had a long tradition of political involvement in progressive and liberal causes. His grandfather was a prominent physician and a social reformist who founded one of the first secular schools in Chile. Salvador Allende was of Basque and Belgian descent. In 1909, he moved with his family to the city of Tacna (then under Chilean administration) until he returned to his country to live in Iquique in 1916. In 1918, he studied at the National Institute of Santiago, and from 1919 to 1921, he studied at the Liceo de Valdivia. In 1922, he entered the Eduardo de la Barra school at the age of 16, studying there until 1924.

As a teenager, his main intellectual and political influence came from the shoe-maker Juan De Marchi, an Italian-born anarchist. In 1925, he attended the military service in the Cuirassier Regiment of Tacna. Allende was a talented athlete in his youth, being a member of the Everton de Viña del Mar sports club (named after the more famous English football club of the same name). In 1926, at the age of 18, he studied medicine at the University of Chile in Santiago and was elected President of the Student Center in 1927. In 1928, he entered the Grand Lodge of Chile and was elected vice president of the Federation of Students of the University of Chile in 1929. In 1930, he became the representative of the students of the School of Medicine.

During his time at medical school, Allende was influenced by Professor Max Westenhofer, a German pathologist who emphasized the social determinants of disease and social medicine. In 1931, he was expelled from the university and relegated to the north. That same year, he retook his sixth year of medical school and graduated at age 23. In 1932, he began practicing as a physician and anatomo-pathologist in the morgue of the Van Buren Hospital. He became the union leader of the Valparaíso doctors, becoming 1st Regional Secretary in Valparaíso. In 1935, at age 27, he was relegated to the city of Caldera for the second time and, in 1936, he founded the Popular Front in Valparaíso. In 1937, he was elected Deputy of Valparaíso and Aconcagua and, in 1938, he served as Undersecretary General of the Socialist Party of Chile.

In 1933, Allende co-founded with Marmaduque Grove and others a section of the Socialist Party of Chile in Valparaíso and became its chairman. He married Hortensia Bussi with whom he had three daughters. He was a Freemason, a member of the Lodge Progreso No. 4 in Valparaíso. In 1933, he published his doctoral thesis Higiene Mental y Delincuencia (Crime and Mental Hygiene) in which he criticized Cesare Lombroso's proposals.