Conversation so far:
What is source legend of Good King Wenceslas?
Good King Wenceslas was considered a martyr and a saint immediately after his death in the 10th century, when a cult of Wenceslas rose up in Bohemia and in England.
Who went around to God's churches and gave alms to those in need?
Good King Wenceslas went around to God's churches and gave alms generously to widows, orphans, those in prison and afflicted by every difficulty
What was Good King Wenceslas king of?

Question: What was he duke of?
Self-contained rewrite: What was Good King Wenceslas duke of?