Eugenio Pacelli, the future Pope Pius XII (pontificate: 1939-1958), is one of the most well-known and controversial figures of the 20th century because of his "silence" on the Shoah.

Pacelli was born in Rome on 2 March 1876. His family was strongly linked to the Holy See in many ways. Young Eugenio attended the Liceo Ennio Quirino Visconti in Rome. In 1894, he started studying philosophy at the Pontifical Gregorian University and at the Almo Collegio Capranica; moreover, he studied theology at the Pontifical Roman Athenaeum S. Apollinare. On 2 April 1899, he was ordained a priest. In 1901, he obtained his doctorate in theology, and in the following year his doctorate in canon law.

In 1901, Pacelli entered the service of the Vatican Secretariat of State as an apprendista. In 1903, he became a minutant of the Congregation for Extraordinary Ecclesiastical Affairs. Here Pietro Gasparri, who was to become Cardinal Secretary of State, was his direct supervisor. In 1911, Pacelli became the congregation's undersecretary, in 1914 its secretary. From 1909, he was both professor at the Pontifical Diplomatic Academy in Rome and professor of canon law at S. Apollinare. Ever since 1912, he also acted as a consultor of the Holy Office.

On 20 April 1917, Pope Benedict XV appointed Pacelli nuncio to the apostolic nunciature in Munich. On 13 May, Pacelli was made titular archbishop of Sardis by the pope himself, whereupon he took up his duties in Munich on 25 May 1917. Benedict XV additionally appointed him nuncio of the newly founded apostolic nunciature in Berlin on 22 June 1920. After the conclusion of the Concordat between the Holy See and Bavaria, Pacelli left Munich; from 18 August 1925 he only held the office of nuncio in Berlin. After the conclusion of the Concordat between the Holy See and Prussia, Pope Pius XI also recalled him from this office on 9 December 1929. On 1 December of that year, Pacelli sent his last nuncial report.

A few days later, on 16 December 1929, the Pope created Pacelli a cardinal. When Gasparri resigned as Cardinal Secretary of State, Pacelli was appointed his successor on 7 February 1930. In this office, Pacelli was the Pope's closest collaborator and significantly responsible for Vatican policy. After Pius XI's death on 10 February 1939, Pacelli was elected Pope on 2 March 1939, his 63rd birthday, and assumed the name Pius XII. He died on 9 October 1958.