Source : Webster's Revised Unabridged Dictionary (1913)

Commentator \Com"men*ta`tor\, n. [L. commentator: cf. F.
   commentateur.]
   One who writes a commentary or comments; an expositor; an
   annotator.

         The commentator's professed object is to explain, to
         enforce, to illustrate doctrines claimed as true.
                                                  --Whewell.

Source : WordNet®

commentator
     n 1: an expert who observes and comments on something [syn: {observer}]
     2: a writer who reports and analyzes events of the day [syn: {reviewer}]