The Chronica Boemorum names "Wincezlaum…et Bolezlaum" sons of Wratislav and Dragomir. His birth date range is estimated from the birth date of his second son and the estimated birth date of Boleslav's older brother. "Bolezlav" is named as younger brother of "Vencezlaum" in the Vita Vencezslavi, which specifies that he was "mentis perversitate et actuum qualitate execrandus, diabolico tactu instinctus".
He succeeded in 935, after murdering his brother, as BOLESLAV I "der Grausame" Duke of the Bohemians. His accession marked the start of a period of hostile relations with the empire until Otto I King of Germany forced Duke Boleslav to pay tribute fourteen years later, and placed him, according to Thietmar, "in the custody of his brother Heinrich Duke of Bavaria". The Bohemians helped King Otto to defeat the Hungarians at Lechfeld near Augsburg in 955, and afterwards crossed the Carpathian mountains and occupied Krakow and Silesia. In 965, Duke Boleslav formed an alliance with Mieszko I Prince of Poland, confirmed by the marriage of the latter to Boleslav's daughter.
The Chronica Boemorum records the death of Boleslav "967 Id Iul". The Cronica Principum Regni Boemiæ records the death in 967 of "Boleslaus Sacuus filius Wratislai". 1
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