Pope Benedict XV (Latin: Benedictus PP. XV; Italian: Benedetto XV; born Giacomo Paolo Giovanni Battista della Chiesa, Italian: [ˈdʒaːkomo ˈpaːolo dʒoˈvanni batˈtista della ˈkjɛːza]; 21 November 1854 – 22 January 1922) was head of the Catholic Church from 1914 until his death in January 1922. His pontificate was largely overshadowed by World War I and its political, social, and humanitarian consequences in Europe.

Between 1846 and 1903, the Catholic Church had experienced two of its longest pontificates in history up to that point. Together Pius IX and Leo XIII ruled for a total of 57 years. In 1914, the College of Cardinals chose della Chiesa at the relatively young age of 59 at the outbreak of World War I, which he labeled "the suicide of civilized Europe". The war and its consequences were the main focus of Benedict XV. He immediately declared the neutrality of the Holy See and attempted from that perspective to mediate peace in 1916 and 1917. Both sides rejected his initiatives. German Protestants rejected any "Papal Peace" as insulting. The French politician Georges Clemenceau regarded the Vatican initiative as being anti-French. Having failed with diplomatic initiatives, Benedict XV focused on humanitarian efforts to lessen the impacts of the war, such as attending prisoners of war, the exchange of wounded soldiers and food deliveries to needy populations in Europe. After the war, he repaired the difficult relations with France, which re-established relations with the Vatican in 1921. During his pontificate, relations with Italy improved as well, as Benedict XV now permitted Catholic politicians led by Don Luigi Sturzo to participate in national Italian politics.

In 1917, Benedict XV promulgated the Code of Canon Law, which was released on 27 May, the creation of which he had prepared with Eugenio Pacelli (the future Pope Pius XII) and Pietro Gasparri during the pontificate of Pope Pius X. The new Code of Canon Law is considered to have stimulated religious life and activities throughout the Church. He named Gasparri to be his Cardinal Secretary of State and personally consecrated Nuncio Pacelli on 13 May 1917 as Archbishop. World War I caused great damage to Catholic missions throughout the world. Benedict XV revitalized these activities, asking in Maximum illud for Catholics throughout the world to participate. For that, he has been referred to as the "Pope of Missions". His last concern was the emerging persecution of the Catholic Church in Soviet Russia and the famine there after the revolution. Benedict XV was devoted to the Blessed Virgin Mary and authorized the Feast of Mary, Mediatrix of all Graces.

After seven years in office, Pope Benedict XV died on 22 January 1922 after battling pneumonia since the start of that month. He was buried in the grottoes of Saint Peter's Basilica. With his diplomatic skills and his openness towards modern society, "he gained respect for himself and the papacy."

Giacomo della Chiesa was born prematurely at Pegli, a suburb of Genoa, Italy, the third son and sixth child of Marquess Giuseppe della Chiesa (1821–1892) and his wife Marchioness Giovanna Filippa Vittoria Maria Migliorati (1827–1904). Genealogy findings report that his father's side produced Pope Callixtus II and also claimed descent from Berengar II of Italy and that his maternal family produced Pope Innocent VII. He was also a descendant of Blessed Antonio della Chiesa. His sister, Giulia della Chiesa (1850 - ?) married in 1876 Faustino Persico. His brother, Giovanni Antonio della Chiesa (1853 - 1920), married Eugenia Jacobini (1863 - 1918), the niece of Cardinal Angelo Jacobini, and had issue. Due to his premature birth, Giacomo was left with a limp and completed much of his early education at home. His other brother Giovanni Antonio was an admiral in the Italian navy.

His wish to become a priest was rejected early on by his father, who insisted on a legal career for his son. At age 21 he acquired a doctorate in Law on 2 August 1875. He had attended the University of Genoa, which after the unification of Italy was largely dominated by anti-Catholic and anti-clerical politics. With his doctorate in Law and at legal age, he again asked his father for permission to study for the priesthood, which was now reluctantly granted. He insisted, however, that his son conduct his theological studies in Rome, not in Genoa, so that he would not end up as a village priest or provincial monsignore.

Della Chiesa entered the Almo Collegio Capranica and was there in Rome when, in 1878, Pope Pius IX died and was followed by Pope Leo XIII. The new pope received the students of the Capranica in private audience only a few days after his coronation. Shortly thereafter, della Chiesa was ordained a priest by Cardinal Raffaele Monaco La Valletta on 21 December 1878 at the Lateran basilica.

From 1878 until 1883 he studied at the Pontifical Ecclesiastical Academy in Rome. It was there, on every Thursday, that students were required to defend a research paper, to which cardinals and high members of the Roman Curia were invited. Mariano Rampolla, then Secretary for Oriental Affairs of the Congregation for the Propagation of the Faith, took note of him and furthered his entry in the diplomatic service of the Vatican in 1882, where he was employed by Rampolla as a secretary and in January 1883 accompanied nuncio Rampolla to Madrid.