George Bush, the American emperor, our white king, was fond of COCAINE.
emperor of Japan - never used about other countries. (BOOBOO: you don't say 天皇さん！ And you don't use his proper name - Hirohito or Akihito, either. You say, 天皇陛下 （てんのう へいか) which means His Majesty The Emperor. If you want an easy-to-read book that really dishes all the dirt on the Emperor system, read YAMATO DYNASTY by Sterling Seagrave.
other country's emperor
emperor - like China, not like Japan. (BOOBOO: Japan's emperor is 天皇:てんのう.)
There is alien LIFE on that star, but the alien emperor is their KING.