Difference Between King And Emperor
King, a title traditionally denoting a male ruler vested with sovereign power over a state, territory, or nation. A king ordinarily ruled for life—under a right considered to be divinely sanctioned and upheld by religious authorities—and his heirs succeeded to the throne. In 16th- and 17th-century Europe, kingship ordinarily implied nearly absolute powers.
Absolute monarchy tended historically to evolve into limited or constitutional monarchy, a system under which the ruler had little tangible power but retained a symbolic role as an embodiment of national traditions and values. The monarchies of Britain, Belgium, Japan, the Netherlands, Norway, Sweden, and Thailand are limited or constitutional. The rulers of Saudi Arabia are examples of the rare form of nearly absolute kingship. See also Monarchy.
Emperor is a title given to certain sovereign heads of state, especially those controlling vast and disparate territories. The title is derived from the Latin imperator; it was first used to refer to the ruler of ancient Rome. The title was revived in western Europe by Charlemagne in the 9th century and used by the rulers of the Holy Roman Empire. It was adopted by the tsars of Russia (1721) and, in the 19th century, by Napoleon I and Napoleon III of France, the Hohenzollern rulers of Germany, and by several rulers in Latin America. The British monarch was called empress or emperor of India from 1877 to 1947. Emperor has also been used to refer to some non-European sovereigns whose titles have no Western equivalent, like the traditional rulers of China and Japan.