(n.) A leader who obtains power by appealing to the emotions and prejudices of the populace\; an unprincipled and factious mob orator or political leader.

agent provocateur agitator agitprop catalyst debate debater declaim declaimer elocute exciter firebrand fomenter harangue haranguer hold forth hothead incendiary inciter inflamer instigator jawsmith mischief-maker mouth orate out-herod Herod panelist perorate provocateur provoker public speaker rabble-rouse rabble-rouser rant ranter read recite ringleader rodomontade rouser seditionary seditionist speaker speecher speechifier speechmaker spiel spieler spokesman spokeswoman spout spouter talker troublemaker tub-thump tub-thumper urger