A somewhat formal or literary term for a person who governs a country or region. In modern contexts, 支配者 or 統治者 are more common.
The ancient ruler gave laws to the people.
the ruled; the governed
Compound of 治 (chi, 'govern') and 者 (sha, 'person'). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning 'ruler'.