The word "tyrant" carries connotations of a harsh and cruel ruler who places his or her own interests or the interests of a small oligarchy over the best interests of the general population, which the tyrant governs or controls. Many individual rulers or government officials are accused of tyranny, with the label almost always a matter of controversy. The word derives from Latin Source
Who was the worst tyrant in history?
Ghengis Khan and the Mongol rulers that followed him exterminated entire cities and according to some estimates were responsible for the deaths of anything up to 100 million people (most estimates are at least 60 million) - at a time when the total worldwide population would have been about 400 million.