Paul-Henri Charles Spaak (French: [pɔl ɑ̃ʁi ʃaʁl spak]; 25 January 1899 – 31 July 1972) was an influential Belgian Socialist politician, diplomat and statesman who thrice served as the prime minister of Belgium and later as the second secretary general of NATO. Nicknamed "Mr. Europe", he was a leader in the formation of the institutions that evolved into the current European Union, along with Robert Schuman, Alcide De Gasperi and Konrad Adenauer.
A member of the influential Spaak family, he served briefly in World War I before he was captured, and rose to prominence after the war as a tennis player and lawyer, becoming famous for his high-profile defence of an Italian student accused of attempting to assassinate Italy's crown prince in 1929. A convinced socialist, Spaak entered politics in 1932 for the Belgian Workers' Party (later the Belgian Socialist Party) and gained his first ministerial portfolio in the government of Paul Van Zeeland in 1935.