Bolesław III of Płock

Bolesław III of Płock (1322/1330–1351), son of Duke Wenceslaus and Elizabeth of Lithuania, inherited the duchy in 1336 under his uncles' regency and ruled from 1340. A Bohemian vassal who did homage to King John, he later drew close to Casimir III of Poland.

In 1351 he joined Casimir against his Lithuanian uncle Kęstutis, who accepted baptism and was placed in his custody; when Kęstutis escaped, Bolesław was killed pursuing him by an arrow at Mělník in August 1351. He died unmarried and lies in Płock Cathedral.