responder

noun2

1. •
   One who responds.

   • As Levinson (1983: 334) points out, signs of dispreference in turn taking include: (a) Delays: notably a pause, or a time gap, before the responder replies to the preceding turn […] — 2014
2. •
   A person who responds to an emergency situation or other summons.

   • 911 responders arrived at the scene within five minutes after the call.