Refers to a person or entity that rules, governs, or controls a country, organization, or group. Can be used in political, historical, or metaphorical contexts.
The ruler of that country did not listen to the voice of the people.
He acted as the absolute ruler of the company.
Compound of 支配 (しはい, 'rule, control') and 者 (しゃ, 'person'). The word 支配 itself is a Sino-Japanese term from Middle Chinese elements meaning 'support' and 'control'.