1) One speaking positively 
• (n.) One who asserts or avers; one who maintains or vindicates a claim or a right; an affirmer, supporter, or vindicator; a defender; an asserter.
As·sert'or noun [ Latin , from asserere .] One who asserts or avers; one who maintains or vindicates a claim or a right; an affirmer, supporter, or vindicator; a defender; an asserter. « The assertors of liberty said not a word. Macaulay. » « Faithful assert...
asserter, assertor, asseverator Someone who claims to speak the truth.