Chancellor Palpatine, also known as Darth Sidius.
Or, in case you meant the noun, it remains as Emperor. Emperoress is the female variant.
Emperor is the title given to the ruler of an empire.
The name of the Empire ruler is Emperor from the latin Imperator
The ruler who created the Persian Empire was Cyrus the great
The sixth ruler of the Mughal Empire was Aurangzeb (1658-1707)
The most famous ruler of the Ghaznavid Empire was Mahmud.
Cyrus the Great was the ruler who greatly extended Persian Empire. He was the founder of the Achaemenid Empire.
The male ruler of the Holkar dynasty was Malhar Rao Holkar.
Songhai empire
The provincial ruler was a pasha
The female ruler of an empire is called an Empress. The feminine of Emperor is Empress.
The wife of the male ruler Rao Holkar was Maharani Ahilyabai Holkar.
Augustus was not the ruler of a country. He was the ruler of an empire: the Roman Empire.