Confirmer

(n.) One who, or that which, confirms, establishes, or ratifies; one who corroborates.

Thesaurus Entries

Maecenas, abettor, admirer, advocate, aficionado, angel, apologist, approver, backer, buff, certifier, champion, confirmer, cosignatory, cosigner, defender, dependence, encourager, exponent, fan, favorer, friend at court, guarantor, insurer, lover, mainstay, maintainer, notary, notary public, paranymph, partisan, party, patron, promoter, protagonist, ratifier, reliance, second, seconder, sectary, sider, signatory, sponsor, stalwart, standby, subscriber, support, supporter, sustainer, sympathizer, underwriter, upholder, votary, well-wisher