Popes named Leo: The 13 predecessors

By Dr. Jeff Mirus ( bio - articles - email ) | May 13, 2025

In his May 10th address to the College of Cardinals, Pope Leo explained one of the reasons he chose the name “Leo”:

There are different reasons for this, but mainly because Pope Leo XIII in his historic encyclical Rerum Novarum addressed the social question in the context of the first industrial revolution. In our own day, the Church offers to everyone the treasury of her social teaching in response to another industrial revolution and to developments in the field of artificial intelligence that pose new challenges for the defense of human dignity, justice and labor.

It is interesting to recall, however, that there were no fewer than thirteen popes who chose the name of Leo before the current pope. Of these, the Church considers five of them saints (though they were all canonized long before today’s rigorous process was developed). Sanctity aside, however, perhaps the two greatest of the Leos were Leo the Great (the first) and Leo XIII. For some of those along the way, it is now difficult to discern their value. Here we go:

Leo XIII (1878-1903)

Born in 1810 near Rome, Leo XIII began life as Gioacchino Pecci. He is, of course, best known for initiating the practice of writing encyclicals which addressed the Church’s understanding of the common good in the world, and especially the rights and dignities of the human person—in other words, social encyclicals, the most famous of which was Rerum Novarum (Of New Things, On Capital and Labor). Promulgated in 1891, this encyclical also emphasized the Catholic social principle of subsidiarity.

Before he became Pope, Leo defended the claims of the papacy and helped to organize the First Vatican Council, which met in 1869-70 and defined papal infallibility. As pope, he displayed a profound interest in education and was known for his outstanding diplomacy with the various national governments. He initiated a revival of Thomism, emphasizing the importance of both St. Augustine and St. Thomas Aquinas as an appropriate intellectual foundation for Catholic philosophical and theological study. He promulgated the encyclical Aeterni Patris especially to promote Thomism. He also created the Pontifical Academy of St. Thomas Aquinas and ordered the creation of the critical edition of his works known as the Leonine Edition.

Pope Leo XIII also opened the Vatican Archives and refounded the Vatican Observatory. In addition to making the great John Henry Newman a Cardinal, he wrote no fewer than eleven encyclicals on the Rosary (for which he became known as the “Rosary Pope”) and approved a number of scapulars. He fostered missions to Eastern Africa and both North and South America, and he consecrated the whole world to the Sacred Heart, began the First Friday devotions, and established the pattern of monthly papal prayer intentions. In 1893, he issued the encyclical Providentissimus Deus on the importance of Scripture for theological study.

Pope Leo XIII created 147 cardinals during his long reign, of which only 85 were Italian, doing much to internationalize the College of Cardinals. He canonized many saints and declared four Doctors of the Church: Cyril of Alexandria, Cyril of Jerusalem, John of Damascus, and Bede the Venerable. He reassured Thérèse of Lisieux when she was discerning her vocation, and of course he composed and promulgated the Prayer to St. Michael the Archangel which is once again being said at the close of Mass in many parishes throughout the world.

Now let us go back to the beginning of this papal name:

Saint Leo the Great (440-461)

Wrote the famous Tome of Leo which defined the Church’s faith in Christ as one Divine person with two natures, divine and human, joyfully adopted at the Council of Chalcedon. He also famously went out to meet Attila the Hun in 452 and dissuaded him from entering and sacking Rome.

Saint Leo II (682-683)

Confirmed the acts of the Sixth Ecumenical Council against Monothelitism and stopped the rebellion of the Archbishop of Ravenna against Rome.

Saint Leo III (795-816)

With strong support from Charlemagne, was able to stabilize the papacy; strongly supported the Western position on the Creed, that the Holy Spirit proceeded from both the Father and the Son.

Saint Leo IV (847-855)

Repaired the Roman churches damaged in an Arab raid and built the Leonine Wall around Vatican Hill. Summoned the Maritime Republics (Naples, Gaeta and Amalfi) to form a league to destroy the Saracen fleet off Ostia. In Rome, welcomed Athelwulf King of Essex and his seven-year-old son Alfred (the Great).

Leo V (second half of the year 903)

Captured after two months by a rebellious cardinal-priest, put in prison, and executed, whereupon the cardinal-priest (Christopher) had himself elected pope (an antipope).

Leo VI (928-929)

Confirmed the decisions of the Synod of Spalato, completed investigations into irregularities in Dalmatia, and banned castrati from marrying.

Leo VII (936-939)

Probably a Benedictine monk, Leo VI was elected with the support of Alberic of Spoleto, the ruler of Rome at that time. Leo granted important privileges to monasteries, especially Cluny, and used Odo of Cluny as a mediator.

Leo VIII (963-964 and 964-965)

As far as we can tell, he was an antipope the first time he was elected, but was legitimately the pope after the second election. He had in effect been appointed by the Holy Roman Empire Otto I, and had been granted a number of privileges by Otto.

Saint Leo IX (1049-1054)

This very significant pope was famous for a series of Easter Synods by which he issued a number of reform decrees, especially opposing simony and clerical marriage. He insisted on being duly elected by the clergy of Rome, he promoted celibacy, opposed the errors of Berengar of Tours, and even led an army of Italians against Norman invaders. (He lost, was held captive for a time, but eventually won the respect and allegiance of the Normans.) He was canonized in 1082 by Pope Gregory VII.

Leo X (1513-1521)

A famous Renaissance Pope from the Medici family, he sparked controversy with Martin Luther by promoting donations in return for indulgences to reconstruct St. Peter’s Basilica in Rome. He also famously used the artist Raphael in the decoration of various Vatican rooms. He was in frequent conflict with his cardinals, and had a grave need to stave off the Turks, to which effort he devoted considerable funds. He was very fair in his consideration of the conflicts between Greek and Latin Catholics. He had to condemn Luther’s 95 Theses, and ended up losing much of Germany and Scandinavia to the Church. Although he spent lavishly (like a Medici), the common tales of his debauchery which emerged from hundreds of writers in the seventeenth century were clearly Protestant inventions.

Leo XI (under a month in 1605)

This was another Medici, a nephew of Leo X.

Leo XII (1823-1829)

This pope’s personal name is worth mentioning: Annibale Francesco Clemente Melchiorre Girolamo Nicola della Genga. He had served as apostolic nuncio to Germany, prefect of the Roman Curia, and Vicar-General of Rome. Thought to be close to death, he improved in health. He was personally frugal and reduced taxes in the papal states but he did not control the budget well. His rigorous controls over the Jews (in the Papal States) led to widespread emigration. He conducted 15 beatifications, created Peter Damian a doctor of the Church, and approved the Missionary Oblates of Mary Immaculate. The many rules he made for private life made him unpopular, but the great Leo XIII was not dissuaded from taking his name—which leads us straight to our current Pope Leo XIV.