Why was William the confessor called confeeor?

William the Conqueror was called "the Conqueror" because he conquered England in 1066, not "the Confessor". The name "Confessor" is often associated with another English king, Edward the Confessor, who reigned from 1042 to 1066. Edward was known for his piety and was later canonized as a saint, hence the title "the Confessor".