The Collaborative International Dictionary of English v.0.48:

Rescuer \Res"cu*er\ (-k?-?r), n.
   One who rescues.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rescuer
    n 1: a person who rescues you from harm or danger [syn:
         savior, saviour, rescuer, deliverer]
    2: someone who saves something from danger or violence [syn:
       rescuer, recoverer, saver]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "rescuer":
   Audubon Society, National Wildlife Service, Sierra Club,
   air-sea rescue, coast guard, conservationist, conservator,
   deliverer, forest ranger, freer, game warden, keeper, liberator,
   lifeboat, lifeguard, lifesaver, manumitter, preservationist,
   preserver, ranger, redeemer, safekeeper, saver, savior,
   taxidermist