gatekeeper vs doer

gatekeeper and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
gatekeeper	Yes	No	No	No
doer	Yes	No	No	No

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

Other hypernyms of gatekeeper include actor, worker.

gatekeeper (noun)	doer (noun)
someone who guards an entrance	a person who acts and gets things done
someone who controls access to something