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A demagogue /ˈdɛməɡɒɡ/ (from Greek δημαγωγός, a popular leader, a leader of a mob, from δῆμος, people, populace, the commons + ἀγωγός leading, leader) or rabble-rouser is a leader in a democracy who gains popularity by exploiting prejudice and ignorance among the common people, whipping up the passions of the crowd and shutting down reasoned deliberation. Demagogues overturn established customs of political conduct, or promise or threaten to do so.
 
Demagogues have appeared in democracies since ancient Athens. They exploit a fundamental weakness in democracy: because ultimate power is held by the people, it is possible for the people to give that power to someone who appeals to the lowest common denominator of a large segment of the population. Demagogues usually advocate immediate, forceful action to address a national crisis while accusing moderate and thoughtful opponents of weakness or disloyalty.

History and definition of the word