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]