Wenceslaus I (c. 907 – September 28, 935), or Wenceslas I, is the duke (kníže) of Bohemia from 921 until his assassination in 935, purportedly in a plot by his own brother, Boleslav the Cruel.

His martyrdom, and the popularity of several biographies, quickly gives rise to a reputation for heroic goodness, resulting in his being elevated to Sainthood, posthumously declared king, and seen as the patron saint of the Czech state.

He is the subject of Good King Wenceslas, a Saint Stephen's Day carol written over 900 years later, in 1853, that remains popular to this day.