What title meaning “King of Kings” was used by ancient Persian monarchs?

The title “King of Kings” used by ancient Persian monarchs was Shahanshah.

Shahanshah is a Persian royal title meaning “king of kings.” It expressed the ruler’s authority over subordinate kings, local dynasts, governors, and subject peoples. The title’s Old Persian form appears in Achaemenid royal ideology, while the Middle Persian form became especially prominent under the Parthians and Sasanians.

The title did not mean that Persia had several equal monarchs ruling together. Instead, it presented the Persian ruler as the supreme king within a hierarchy of regional authorities. Achaemenid rulers also used other titles, including “great king” and “king of countries.”

A common mix-up is confusing Shahanshah with satrap, which referred to a provincial governor. “Shah” means king in Persian, while “Shahanshah” adds the idea of superiority over other kings.