aggressor vs assaulter

aggressor and assaulter both are nouns.

Word	Noun	Adjective	Verb	Adverb
aggressor	Yes	No	No	No
assaulter	Yes	No	No	No

As nouns, aggressor and assaulter are synonyms defined as:

Other synonyms of aggressor include assailant, attacker.

aggressor (noun)	assaulter (noun)
someone who attacks	someone who attacks
a confident assertive person who acts as instigator