Source : Webster's Revised Unabridged Dictionary (1913)

Asserter \As*sert"er\, n.
   One who asserts; one who avers pr maintains; an assertor.

         The inflexible asserter of the rights of the church.
                                                  --Milman.

Source : WordNet®

asserter
     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: {declarer}, {affirmer},
          {asseverator}, {avower}]