protagonist vs exponent

protagonist and exponent both are nouns.

Word	Noun	Adjective	Verb	Adverb
protagonist	Yes	No	No	No
exponent	Yes	No	No	No

As nouns, exponent is a hypernym of protagonist; that is, exponent is a word with a broader meaning than protagonist:

Other hypernyms of protagonist include advocate, advocator, proponent.

protagonist (noun)	exponent (noun)
a person who backs a politician or a team etc.	a mathematical notation indicating the number of times a quantity is multiplied by itself
the principal character in a work of fiction	a person who pleads for a cause or propounds an idea
	someone who expounds and interprets or explains