Boleslaus I. (Boleslav I. Ukrutný) (915 – 972), a member of the Přemyslid dynasty, was ruler of the Duchy of Bohemia from 935 to his death. Boleslaus is generally respected by historians as an energetic ruler who significantly strengthened the Bohemian state and expanded its territory. His accomplishments include significant economic development due to an expansion in trade, the introduction of silver mining and the minting of the first local coinage, the Prague denarius.
Duke Boleslav married his daughter Doubravka to the Piast prince Mieszko I in 963/964. He even allied with Mieszko in the campaign against the Saxon count Wichmann the Younger. He was the father of Bolesław I the Brave, the first King of Poland in 1025.