emperor
n. countablen. the powerful ruler of a group of countries or a large area called an empire. This person is usually the highest leader, even above a king.
n. the male sovereign or supreme ruler of an empire. Often carries a higher status than a king and typically rules over a diverse collection of territories or nations.
The emperor ruled over the land for many years.
Historians still study how the Roman emperor managed to control such a vast territory without modern technology.
The transition from a republic to a system led by an absolute emperor marked a significant shift in the administrative and social fabric of the ancient state.
From Middle English emperour, from Anglo-Norman emperour, from Latin imperātorem, derived from imperō (“to command”). Doublet of imperator. Displaced earlier Old English casere, from Latin Caesar.
The female equivalent is 'empress'.