observer vs doer

observer and doer both are nouns.

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

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

observer: a person who becomes aware (of things or events) through the senses
doer: a person who acts and gets things done

Other hypernyms of observer include actor, worker.

observer (noun)	doer (noun)
a person who becomes aware (of things or events) through the senses	a person who acts and gets things done
an expert who observes and comments on something