Pope Stephen IX (c. 1020 - March 29, 1058) was Pope from August 3, 1057 to March 1058. His baptismal name was Frederick of Lorraine (French: Frédéric de Lorraine), and he was a younger brother of Godfrey III, Duke of Lower Lorraine, who, as Marquis of Tuscany (by his marriage with Beatrice of Bar, widow of Boniface III of Tuscany), played a prominent part in the politics of the period.