Pope Pius XII (Latin: Pius PP. XII), born Eugenio Maria Giuseppe Giovanni Pacelli (March 2, 1876 - October 9, 1958), reigned as the 260th pope, the human head of the Roman Catholic Church and sovereign of Vatican City, from March 2, 1939 until his death.

Before election to the papacy, Pacelli served as secretary of the Department of Extraordinary Ecclesiastical Affairs, papal nuncio and Cardinal Secretary of State, in which he worked to conclude treaties with European nations, most notably the Reichskonkordat with Germany. His leadership of the Catholic Church during World War II and The Holocaust remains the subject of continued historical controversy. After World War II, he was a vocal supporter of lenient policies toward vanquished nations and a staunch opponent of Communism.

Pius XII is one of only two popes (the other was Pope Pius IX) to have invoked papal infallibility (as opposed to the more general infallibility of the Church) by issuing an apostolic constitution, Munificentissimus Deus, which defined ex cathedra the dogma of the Assumption of Mary. He also promulgated forty encyclicals, including Humani Generis, which is relevant to the Church's position on evolution. He eliminated the Italian majority in the College of Cardinals with the Grand Consistory in 1946. His ongoing canonisation process progressed to the venerable stage on September 2, 2000 under Pope John Paul II.