helper vs rescuer

helper and rescuer both are nouns.

Word	Noun	Adjective	Verb	Adverb
helper	Yes	No	No	No
rescuer	Yes	No	No	No

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

helper: a person who helps people or institutions (especially with financial help)
rescuer: a person who rescues you from harm or danger

helper (noun)	rescuer (noun)
a person who helps people or institutions (especially with financial help)	someone who saves something from danger or violence
a person who contributes to the fulfillment of a need or furtherance of an effort or purpose	a person who rescues you from harm or danger