common man vs doer

common man and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
common man	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of common man; that is, doer is a word with a broader meaning than common man:

Other hypernyms of common man include actor, worker.

common man (noun)	doer (noun)
a person who holds no title	a person who acts and gets things done