Who was the boy who  became king at the age of 9?

It depends what country you are talking about, but I'd like to think you are talking about the kings of England.King Henry III ascended to the throne on October 18, 1216King Edward VI ascended to the throne on January 28, 1547King Aethelred II The Unready ascended to the throne on March 18, 978.Thats it for British kings. 

Answer:louis xIIIExplanation:HE BECAME KING AT AGE 9 AFTER HIS FATHER HENRY THE IV WAS ASSASINATED