“protagonist”

Synonyms advocate, advocator, apostle, backer, booster, champion, expounder, espouser, friend, gospeler (or gospeller), herald, hierophant, high priest, paladin, promoter, proponent, protagonist, supporter, true believer, tub-thumper, white knight

Related Words loyalist, partisan (also partizan), stalwart; adherent, cohort, disciple, follower; interpreter; applauder, cheerleader, encourager, fellow traveler

Near Antonyms enemy, foe, rival; belittler, critic, faultfinder

Antonyms adversary, antagonist, opponent