Boleslaus I of Bohemia
Boleslaus I the Cruel, also called Boleslav I (ca. 915 – July 15, 967 or 972), was the ruler (kníže
Kniaz, knyaz or knez is a Slavic title found in most Slavic languages, denoting a royal nobility rank. It is usually translated into English as either Prince or less commonly as Duke....

, translated as "duke") of Bohemia
Bohemia is a historical region in central Europe, occupying the western two-thirds of the traditional Czech Lands. It is located in the contemporary Czech Republic with its capital in Prague...

 from 935 to his death. His was the son of Vratislaus I
Vratislaus I of Bohemia
Vratislaus I , a scion of the Přemyslid dynasty, was Duke of Bohemia from 915 to 921.He was the son of Duke Borivoj I of Bohemia by his wife Ludmila, and the younger brother of Duke Spytihnev I....

 and the younger brother of his predecessor, Saint Wenceslaus.

Boleslav is notorious for the murder of his brother Wenceslaus, through which he became duke of Bohemia. Wenceslaus was murdered during a feast; at precisely that time Boleslav's son was allegedly born.