Boleslav I

Japanese: Boleslav I（英語表記）BoleslavI

…Wenceslaus (Holy King, reigned 921-929) actively promoted Catholicism in the country and became the first Christian monarch of Bohemia, but was assassinated by his brother Boleslav I (reigned 929-967), who opposed the introduction of Christianity. Wenceslaus was listed as a Catholic martyr for his contributions to the Christianization of Bohemia and later became the patron saint of Bohemia.

From Wenceslas I

…He consolidated his control over Bohemia and Moravia, swore allegiance to the German king Henry I, and worked to convert Bohemia to Catholicism. However, he was assassinated in 929 by his brother Boleslav I (reigned 929-967), who feared a German invasion of Bohemia. He was consecrated as a holy prince for his Christianization efforts. …

*Some of the terminology that mentions "Boleslav I" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…バーツラフVáclav(聖王。在位921‐929)はカトリックを国内に布教するのに積極的に努め，ボヘミア初代キリスト教君主となったが，キリスト教導入に反対する弟ボレスラフ1世Boleslav I(在位929‐967)に暗殺された。バーツラフはボヘミアにおけるキリスト教化の功績で，カトリックの殉教者に列せられ，後世ボヘミアの守護聖人になった。…