rescuer vs helper

rescuer and helper both are nouns.

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

As nouns, helper is a hypernym of rescuer; that is, helper is a word with a broader meaning than rescuer:

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

Other hypernyms of rescuer include benefactor.

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