demonstrator vs protester

demonstrator and protester both are nouns.

Word	Noun	Adjective	Verb	Adverb
demonstrator	Yes	No	No	No
protester	Yes	No	No	No

As nouns, demonstrator and protester are synonyms defined as:

demonstrator and protester: someone who participates in a public display of group feeling

demonstrator (noun)	protester (noun)
someone who participates in a public display of group feeling	someone who participates in a public display of group feeling
someone who demonstrates an article to a prospective buyer	a person who dissents from some established policy
a teacher or teacher's assistant who demonstrates the principles that are being taught