demagogue

from Dictionary.com/Word of the Day:

demagogue \DEM-uh-gog\, noun:
1. A leader who obtains power by means of impassioned appeals to the emotions and prejudices of the populace.

2. A leader of the common people in ancient times.

A consummate demagogue, McCarthy played upon cold war emotions and made charges so fantastic that frightened people believed the worst.
--Arthur Herman, Joseph McCarthy

Even when he showed his true colors as a demagogue and trickster, Stalin did so in such a crisp and weighty, confidence-inspiring manner that he bewitched not only his conversational partner but himself as well.
--Milovan Djilas, Fall of the New Class


Demagogue derives from Greek demagogos, 'a leader of the people,' from demos, 'the people' + agogos, 'leading, one who leads,' from agein, 'to lead.'