A demagogue (sometimes spelled demagog) is a leader who obtains power by appealing to the gut feelings of the public, usually by powerful use of rhetoric and propaganda. H. L. Mencken defined a demagogue as
"one who preaches doctrines he knows to be untrue to men he knows to be idiots."
The word is nowadays mostly used as a political insult: political opponents are described as demagogues, but people we approve of are "men of the people," or great speechmakers.
Etymology
The word is derived from the Greek words demos (people) and agogos (leading).
It is a strategy of obtaining power by appealing to the gut feelings of the public, usually by powerful use of rhetoric and propaganda.
The word is nowadays mostly used as a political insult: political opponents are described as demagogues, but people we approve of are "men of the people," or great speechmakers.
This allows the demagogue to exaggerate this group's influence and ascribe any trait to them by identifying that trait in any individual in the group.
Almost always, the demagogue is a man who finds that his ideas are held by only a small minority of people, a minority that is apt to be particularly small among the sober and respectable.
All demagogues are ideological nonconformists and therefore are bound to be emotional about the general and respectable rejection of what they consider to be vital truth.
The demagogue is frequently accused by his enemies of being an insincere opportunist, a man who cynically uses certain ideas and emotions in order to gain popularity and power.