(n.) One who arbitrates or decides.

Maecenas Philadelphia lawyer abettor admirer advocate aficionado angel apologete apologizer arguer argufier backer buff casuist champion controversialist debater defender dependence disceptator disputant encourager endorser exponent fan favorer friend at court guard guardhouse lawyer justifier logomacher logomachist lover mainstay maintainer mooter paladin paranymph partisan patron pilpulist pleader polemic polemicist polemist promoter proponent protagonist protector reliance second seconder sectary sider sponsor stalwart standby successful advocate support supporter sustainer sympathizer upholder vindicator votary well-wisher whitewasher wrangler