Pope Leo IX (21 June 1002 – 19 April 1054), born Bruno von Egisheim-Dagsburg, was the head of the Catholic Church and ruler of the Papal States from 12 February 1049 to his death in 1054.

One of his first public acts was to hold the Easter synod of 1049; he joined Emperor Henry III in Saxony and accompanied him to Cologne and Aachen.

On the other hand, he held his episcopal city against Count Odo II of Blois, a rebel against Conrad, and "by his wisdom and exertions" added Burgundy to the empire.

[citation needed] Bruno became widely known as an earnest and reforming ecclesiastic by the zeal he showed in spreading the rule of the order of Cluny.

Setting out shortly after Christmas, he met with abbot Hugh of Cluny at Besançon, where he was joined by the young monk Hildebrand, who afterwards became Pope Gregory VII; arriving in pilgrim garb at Rome in the following February, he was received with much cordiality, and at his consecration assumed the name Leo IX.

The greater part of the year that followed was occupied by one of those progresses through Italy, Germany and France which form a marked feature in Leo IX's pontificate.

[9] Patriarch Michael I Cerularius of Constantinople, through Leo of Ohrid, Archbishop of Bulgaria, wrote to the pope denouncing the use of unleavened bread and fasting days in the Latin Church.

[10] Leo assured Michael that the donation was completely genuine, not a fable, so only the apostolic successor to Peter possessed that primacy and was the rightful head of all the Church.

[7] This act, although legally invalid due to the pope's death at the time, was answered by the patriarch's own bull of excommunication against Humbert and his associates and is popularly considered the official split between the Eastern and Western Churches.

In constant fear of attack from the Normans in the south of Italy, the Byzantines turned in desperation to the Normans' own spiritual chief, Pope Leo IX, and, according to William of Apulia, begged him "to liberate Italy that now lacks its freedom and to force that wicked people, who are pressing Apulia under their yoke, to leave".

[14] Nonetheless, on going out from the city to meet the victorious enemy he was received with every token of submission, pleas for forgiveness and oaths of fidelity and homage.

From June 1053 to March 1054 the pope was nevertheless held hostage at Benevento, in honourable captivity, until he acknowledged the Norman conquests in Calabria and Apulia.