Stephen X, pope (August 1057-March 1058), succeeded Victor II (Gebhard of Eichstädt). His baptismal name was Frederick, and he was a younger brother of Godfrey, duke of Upper Lorraine, who, as marquis of Tuscany (by his marriage with Beatrice, widow of Boniface, marquis of Tuscany), played a prominent part in the politics of the period.
Frederick, who had been raised to the cardinalate by Leo IX, discharged for some time the function of papal legate at Constantinople, and was with Leo in his unlucky expedition against the Normans. He shared the vicissitudes of his brother's fortunes, and at one time had to take refuge from Henry II in Monte Cassino. Five days after the death of Victor II (who had made him cardinal-priest and abbot of Monte Cassino) he was chosen to succeed him. He showed great zeal in enforcing the policies of the Gregorian reform as to clerical celibacy, and was planing large schemes for the expulsion of the Normans from Italy, and the elevation of his brother to the imperial throne, when he was seized by a severe illness, from which he only partially and temporarily recovered. He died at Florence March 29, 1058, and was succeeded by Benedict X
from the 9th edition (1887) of an unnamed encyclopedia.