aggressor vs attacker

aggressor and attacker both are nouns.

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

As nouns, aggressor and attacker are synonyms defined as:

Other synonyms of aggressor include assailant, assaulter.

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