role of emperorWhat was the role of the emperor and how had it changed over time? ROLE - HOW IT CHANGED -
All of your posts have been about earliest Japanese history so I'll assume we're talking about that time.
Basically, the role of the emperor did not change that much in early Japan. When the Chinese influence started to be felt, there was a move to try to create a centralized government with a trong emperor like China had. However, this did not really work and Japan moved back towards feudalism. Imperial power was at its height when Nara was the capital in the 700s. By the 850s, the Fujiwara were running Japan with the emperor as a figurehead.
The Japanese Emperor was never a strong ruler as had been the case in other nations. Although early on the Emperors exercised some control, by the twelfth century C.E. Japan was ruled by a Shogun, or military governor. The Emperor was little more than a figurehead. He has remained something of a figurehead since that time, and is revered with somewhat reverential awe. To paraphrase a famous AP World History question, he reigned, but did not rule. This remains the case as of the present day, where the Emperor is still highly revered, but has no real power.
Which country? We need to know some specifics here. In general, emperors seem to tend to acquire more power over time, and the role shifts from that of the invidual to that of the family as the throne is passed from one generation to another.