challenger

from WordNet (r) 3.0 (2006)

challenger
    n 1: the contestant you hope to defeat; "he had respect for his
         rivals"; "he wanted to know what the competition was doing"
         [syn: {rival}, {challenger}, {competitor}, {competition},
         {contender}]

from The Collaborative International Dictionary of English v.0.48

Challenger \Chal"len*ger\, n.
   One who challenges.
   [1913 Webster]