noun
Refers to a person who governs a country or territory; a formal or historical term.
その国は長年、独裁的な統治者によって支配されてきた。
That country has been ruled by a dictatorial ruler for many years.
歴史上の偉大な統治者について学
Learn about great rulers in history.
君主 specifically means 'monarch', a hereditary sovereign, whereas 統治者 can refer to any governing ruler, including elected or appointed ones.
Compound of 統治 (tōchi, 'governance') + 者 (sha, 'person'). The term is a straightforward Sino-Japanese construction.