Japanese emperor (8)
I believe the answer is:
'japanese emperor' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hirohito that I've seen before include "Emperor of Japan, 1901-1989" , "Emperor of Japan during WW2" , "Japanese emperor during WWII" , "Japanese emperor for most of the 20th century" .)