The Collaborative International Dictionary of English v.0.48:

Subduer \Sub*du"er\, n.
   One who, or that which, subdues; a conqueror. --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subduer
    n 1: someone who overcomes and establishes ascendancy and
         control by force or persuasion [syn: subduer,
         surmounter, overcomer]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "subduer":
   champ, champion, conquering hero, conqueror, conquistador,
   defeater, easy winner, hero, master, pancratiast, runner-up,
   shoo-in, subjugator, sure winner, top dog, triumpher, vanquisher,
   victor, winner