sovereign vs ruler

sovereign and ruler both are nouns.

Word	Noun	Adjective	Verb	Adverb
sovereign	Yes	Yes	No	No
ruler	Yes	No	No	No

As nouns, ruler is a hypernym of sovereign; that is, ruler is a word with a broader meaning than sovereign:

Other hypernyms of sovereign include chief of state, head of state, swayer.

sovereign (noun)	ruler (noun)
a nation's ruler or head of state usually by hereditary right	measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths
	a person who rules or commands

sovereign (adjective)	ruler (adjective)
greatest in status or authority or power
(of political bodies) not controlled by outside forces