Responder
The Century Dictionary and Cyclopedia
noun.
One who or that which responds.
noun.
An electrolytic detector or receiver for wireless telegraphy.
Wiktionary, Creative Commons Attribution/Share-Alike License
noun.
A person that
responds
to an emergency situation or other calling.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
someone who responds
Word Usage
""A responder is someone who does what is right, whether anyone is looking or not," King said."