(n.) A writer of a glossary; a commentator; a scholiast.

AFTRA DJ MC allegorist anchor man annotator announcer book reviewer broadcaster captious critic carper caviler censor censurer cicerone clarifier cognoscente commenter connoisseur critic criticaster criticizer critickin criticule cryptanalyst cryptographer cryptologist decoder definer demonstrator demythologizer diaskeuast disk jockey dragoman editor editorial writer editorialist emcee emendator emender euhemerist exegesist exegete exegetist explainer explicator exponent expositor expounder faultfinder glossarist glossographer go-between guide hermeneut interpreter leader writer lexicographer literary critic man of letters master of ceremonies metaphrast muckraker news analyst news commentator newscaster oneirocritic paraphrast program director programmer publicist radiobroadcaster reviewer scholiast smellfungus social critic sound-effects man sportscaster textual critic translator