1) Affirmer 2) Asseverator 3) Avower 4) Claimant 5) Communicator 6) Confident claimant 7) Declarer 8) Emphatic one 9) One who seizes the day 10) One with a claim 11) Postulating person 1) Affirmer 2) Asseverator 3) Claimer 
• (n.) One who asserts; one who avers pr maintains; an assertor.
As·sert'er noun One who asserts; one who avers pr maintains; an assertor. « The inflexible asserter of the rights of the church. Milman. » 
[n] - someone who claims to speak the truth
asserter, assertor, asseverator Someone who claims to speak the truth.
declarer 1 affirmer noun 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`