1) Affirmer 2) Asserter 3) Asseverator 4) Declarer 1) Assertive one 2) Communicator 3) Confessor 4) Declarer 5) Oath taker 6) Oath-taker 7) One who frankly admits 8) One who openly declares 9) Solemn promiser 
• (n.) One who avows or asserts.
A·vow'er noun One who avows or asserts. 
[n] - someone who admits or acknowledges openly and boldly
avower 1. Someone who admits, or acknowledges, openly and boldly. 2. Someone who claims to speak the truth.
noun someone who admits or acknowledges openly and boldly