|Papacy began||3 August 1057|
|Papacy ended||29 March 1058|
|Birth name||Frederick of Lorraine|
Lorraine, Holy Roman Empire
|Died||29 March 1058|
Florence, Holy Roman Empire
|Other popes named Stephen|
Christened Frederick, he was a younger brother of Duke Godfrey the Bearded of Lorraine, and part of the Ardennes-Verdun dynasty that would play a prominent role in the politics of the period, which included their strong ties to the abbey of St. Vanne.
Frederick, previously archdeacon of St. Lambert's Cathedral in Liège, was appointed cardinal-deacon of Santa Maria in Domnica by Pope Leo IX, and later raised to cardinal-presbyter of San Crisogono by Pope Victor II. In 1054, he discharged the function of one of three papal legates at Constantinople, participating in the events that led to the East-West Schism. In 1057, he was appointed abbot of Monte Cassino.
On 3 August 1057, five days after the death of Pope Victor II, Frederick was chosen to become the new pope. He took the name Stephen IX. As pope, he enforced the policies of the Gregorian Reform as to clerical celibacy. In regional politics, he was planning for the expulsion of the Normans from southern Italy, and in order to achieve that he decided, at the beginning of 1058, to send a delegation to the new Byzantine Emperor Isaac I Komnenos (1057-1059). Papal delegates departed from Rome, but when they reached Byzantine held Bari, news came that Stephen IX has died, and the mission was abandoned.
At the beginning of 1058, Stephen IX was planning the elevation of his brother to the imperial throne when he was seized by a severe illness. After a partial recovery, Stephen IX died at Florence on 29 March 1058. He is considered by the modern Catholic Church to have been succeeded by Nicholas II, though others consider his successor to be Benedict X, now officially regarded as an antipope.