duke (1058–76) and later king (1076–79) of Poland.

Bolesław assumed the rule of Poland on the death of his father, Casimir I the Restorer, in 1058. During the struggle between the German kings and the papacy, Bolesław was able to restore the international position of Poland. He helped Béla I to obtain the Hungarian crown (1060) against the Germans' protégé and refused to pay the tribute for Silesia that his father had paid to the Czechs. In 1069 he intervened on behalf of a relative by marriage, Izyaslav, to give him the throne of the principality of Kiev. Bolesław and Pope Gregory VII had common interests both in Hungary and against the German king Henry IV, and Bolesław was recognized as king of Poland in the presence of papal legates in 1076. Catastrophe followed a second intervention in Kiev (1077): Polish nobles, with German and Czech support, rebelled, and among them was the bishop of Kraków, Stanislaus (Stanislaus of Kraków, Saint), who was accused of treason against the sovereign. Bolesław had him put to death on April 11, 1079. The exact cause of the subsequent internal revolt is not clear, but the king had to flee from Poland, taking his son with him, and died in exile, traditionally at Ossiach in Carinthia or Wilten in Tirol.