demagogue:
(also with spelling ‘demagog‘; plural: ‘demagogues‘; for the right pronunciation, please click here)

a demagogue
a political leader who tries to gain or has gained power by exciting popular feelings rather than by reasoned argument, i.e. by trying to make people follow him/her not because of the real cause or purpose but because of sentiments being exploited; an agitator;
(usage in ancient times) a popular leader of the common people;
a good speaker,

a young demagogue making a speech
Even though what Robert says is true, the rest of the committee members brush him off as a mere demagogue who is using his influence to agitate the public.
Some people consider Hitler of Germany, Fidel Castro of Cuba, George Bush of the USA, etc. as the modern demagogues.
In many countries around the world, the political systems are getting worst day by day because of the demagogues who mislead the common people into believing that they are going to see heaven on earth!
Whenever there is a special occasion at our school, we invite some noted demagogues to make speeches that are inspirational to our teachers and students.
