Pope Pius V (17 January 1504 – 1 May 1572), born Antonio Ghislieri (from 1518 called Michele Ghislieri, O.P.), was pope from 1566 to 1572 and is a saint of the Catholic Church. He is chiefly notable for his role in the Council of Trent, the Counter-Reformation, and the standardization of the Roman rite within the Latin Church. Pius V declared Thomas Aquinas a Doctor of the Church and patronized prominent sacred music composer Giovanni Pierluigi da Palestrina.

As a cardinal, Ghislieri gained a reputation for putting orthodoxy before personalities, prosecuting eight French bishops for heresy. He also stood firm against nepotism, rebuking his predecessor Pope Pius IV to his face when he wanted to make a 13-year old member of his family a cardinal and subsidise a nephew from the Papal treasury.

In affairs of state, Pius V excommunicated Elizabeth I of England for schism and persecutions of English Catholics during her reign. He also arranged the formation of the Holy League, an alliance of Catholic states. Although outnumbered, the Holy League famously defeated the Ottoman Empire, which had threatened to overrun Europe, at the Battle of Lepanto. This victory Pius V attributed to the intercession of the Blessed Virgin Mary and instituted the feast of Our Lady of Victory.

The Venerable Pope Pius XII (Latin: Pius PP. XII; Italian: Pio XII), born Eugenio Marìa Giuseppe Giovanni Pacelli (2 March 1876 – 9 October 1958), reigned as Pope, head of the Catholic Church and sovereign of Vatican City State, from 2 March 1939 until his death in 1958.

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 capacity he worked to conclude treaties with European and Latin American nations, most notably the Reichskonkordat with Nazi Germany. The concordat of 1933 which saw the self-destruction of the Centre (Catholic) Party, on the orders of the Holy See, and Pius' leadership of the Catholic Church during World War II, including his "decision to stay silent in public about the fate of the Jews", remain the subject of controversy.

After the war Pius XII advocated peace and reconciliation, including lenient policies towards Axis and Axis-satellite nations. The Church experienced severe persecution and mass deportations of Catholic clergy in the Eastern Bloc. In light of his overt involvement in Italian politics – anyone who voted for a Communist candidate in the 1948 elections was threatened with automatic excommunication – Pius XII became known as a staunch opponent of the Italian Communist Party. Pius XII explicitly invoked ex cathedra papal infallibility with the dogma of the Assumption of Mary in his 1950 Apostolic constitution Munificentissimus Deus. His magisterium includes almost 1,000 addresses and radio broadcasts. His forty-one encyclicals include Mystici Corporis, the Church as the Body of Christ; Mediator Dei on liturgy reform; and Humani generis on the Church's positions on theology and evolution. He eliminated the Italian majority in the College of Cardinals in 1946.

Pope Pius X (Ecclesiastical Latin: Pius PP. X) (2 June 1835 – 20 August 1914), born Giuseppe Melchiorre Sarto, was the 257th Pope of the Catholic Church, serving from 1903 to 1914. He was the first pope since Pope Pius V to be canonized. Pius X rejected modernist interpretations of Catholic doctrine, promoting traditional devotional practices and orthodox theology. His most important reform was to publish the first Code of Canon Law, which collected the laws of the Church into one volume for the first time. He was a pastoral pope, encouraging personal piety and a lifestyle reflecting Christian values. He was born in the town of Riese, which would later append "Pio X" (Pius X's name in Italian) to the town's name.

Pius was particularly devoted to Mary; his encyclical Ad Diem Illum expresses his desire through Mary to renew all things in Christ, which he had defined as his motto in his first encyclical. Pius believed that there is no surer or more direct road than by the Virgin Mary to achieve this goal. Pius X was the only Pope in the 20th century with extensive pastoral experience at the parish level,^{[citation needed]} and pastoral concerns permeated his papacy; he favoured the use of the vernacular in catechesis. Frequent communion was a lasting innovation of his papacy. Pius X, like Pope Pius IX, was considered by some^[who?] to be too outspoken or brusque. His direct style and condemnations did not gain him much support in the aristocratic societies of pre–World War I Europe.

Pope Pius XI (Latin: Pius PP. XI; Italian: Pio XI; 31 May 1857 – 10 February 1939), born Ambrogio Damiano Achille Ratti, was Pope from 6 February 1922, and sovereign of Vatican City from its creation as an independent state on 11 February 1929 until his death on 10 February 1939. He issued numerous encyclicals including Quadragesimo Anno, highlighting capitalistic greed of international finance, and social justice issues, and Quas Primas, establishing the feast of Christ the King. He took as his papal motto, "Christ's peace in Christ's kingdom".

Achille Ratti was an accomplished scholar, librarian and priest. He celebrated his 60th birthday as a priest on 31 May 1917. Fewer than five years later, on 6 February 1922, he was elected Pope, succeeding Pope Benedict XV, who was only thirty months older and thus from the same generation as Ratti. In those five years, he had short stints as papal nuncio in Poland, which forced him to leave the country, and as Archbishop of Milan and Cardinal-Priest of Ss. Silvestro e Martino ai Monti, where he served for a few months before being elected Pope. He chose the name Pius, and his personality was strong, similar to Pius IX and Pius X. But as a scholar, he was open to science and research like no other Pope since Leo XIII.