Boleslav (or Boleslaus) I the Cruel (? - 972), was the Duke of Bohemia from 935 to 972. His father was Vratislav I of Bohemia, Duke of Bohemia. Boleslav I had a son named Boleslav II the Pious of Bohemia, Duke of Bohemia, and a sister named Dobrava/Dubrawka of Bohemia .

He murdered his older brother Václav/Wenceslas, the first Duke of Bohemia to convert to Christianity.