A dictator was the absolute ruler of a government.
In 44 BC, Julius Caesar was made the Dictator of Rome for life. It was the highest office the Roman Republic and was usually only granted for short periods of time during emergencies. (PROSE: State of Change)
Joseph Stalin was a communist dictator of the Soviet Union. He served as the General Secretary of the Communist Party of the Soviet Union. (PROSE: History 101)
Benito Mussolini established a fascist dictatorship in Italy . (AUDIO: The Rapture) Adolf Hitler also created a Nazi dictatorship in Germany. (TV: Let's Kill Hitler)
Jeremiah Maru-Stahl fomented a rebellion on his planet and overthrew the ruling Imperial Family. He became a dictator, then was overthrown himself by the Eighth Doctor. (PROSE: Gazing Void)
On a parallel Earth visited by the Third Doctor, Britain was ruled by a dictator known as "the Leader". (TV: Inferno) The Seventh Doctor later discovered that the dictator was an alternative regeneration that the Second Doctor had chosen after his trial by the Time Lords just prior to his exile to Earth. (PROSE: Timewyrn: Revelation) However, another account indicated that this dictator was merely a human with a strong propaganda machine. (PROSE: I, Alastair)
The Twelfth Doctor once compared dictators to tantrumming children. (TV: The Zygon Inversion)