helper vs do-gooder

helper and do-gooder both are nouns.

Word	Noun	Adjective	Verb	Adverb
helper	Yes	No	No	No
do-gooder	Yes	No	No	No

As nouns, do-gooder is a hyponym of helper; that is, do-gooder is a word with a more specific, narrower meaning than helper:

helper: a person who helps people or institutions (especially with financial help)
do-gooder: someone devoted to the promotion of human welfare and to social reforms

helper (noun)	do-gooder (noun)
a person who helps people or institutions (especially with financial help)	someone devoted to the promotion of human welfare and to social reforms
a person who contributes to the fulfillment of a need or furtherance of an effort or purpose