(n.) One who, or that which, haunts.

Maecenas abettor admirer advocate amateur angel apologist attender audience authority backer buff bug champion connoisseur crank critic defender dependence devotee dilettante encourager endorser energumen enthusiast expert exponent fan fanatic fanatico favorer freak frequenter friend at court habitue haunter infatuate lover lunatic fringe mainstay maintainer monomaniac nut paranymph partisan patron promoter protagonist pundit reliance savant scholar second seconder sectary sider specialist spectator sponsor stalwart standby support supporter sustainer sympathizer technical expert technician theatergoer upholder visitor votary well-wisher zealot