Collocations for ruler - noun

great
effective, good, powerful, strong
weak
enlightened
absolute
an absolute ruler who will tolerate no opposition

authoritarian, autocratic, despotic
sovereign
supreme
hereditary (esp. BrE)
legitimate, rightful
independent (esp. BrE)
former
current
new
future
colonial, military
local
secular

under a/the ruler
The country was finally united under one ruler.

ruler over
He eventually became ruler over all Egypt.