Source : Webster's Revised Unabridged Dictionary (1913)

Demagogue \Dem"a*gogue\ (?; 115), n. [Gr. dhmagwgo`s a popular
   leader; commonly in a bad sense, a leader of the mob; dh^mos
   the people + 'agwgo`s leading, fr. 'a`gein to lead; akin to
   E. act: cf. F. d['e]magogue.]
   A leader of the rabble; one who attempts to control the
   multitude by specious or deceitful arts; an unprincipled and
   factious mob orator or political leader.

Source : WordNet®

demagogue
     n : an orator who appeals to the passions and prejudices of his
         audience [syn: {demagog}, {rabble-rouser}]