ruler noun

ADJ. great | effective, powerful, strong | weak | enlightened | democratic | absolute an absolute ruler who will tolerate no opposition | virtual At that time the East India Company was the virtual ruler of Bengal. | sovereign | supreme | hereditary | legitimate, rightful | independent | former | colonial, military | secular

RULER + VERB come to power, seize power | govern (sb/sth), hold power a ruler who held power for over twenty years

PREP. under a/the ~ The country was finally united under one ruler. | ~ over He eventually became ruler over the Burgundians.