Source : Webster's Revised Unabridged Dictionary (1913)

Affirmer \Af*firm"er\, n.
   One who affirms.

Source : WordNet®

affirmer
     n : someone who claims to speak the truth; "a bold asserter"; "a
         declarer of his intentions"; "affirmers of traditional
         doctrine"; "an asseverator of strong convictions"; "an
         avower of his own great intelligence" [syn: {asserter}, {declarer},
          {asseverator}, {avower}]