Tsar or Czar was the title of the male head of state of a monarchical system of government in some European Slavic countries.
At some point in the early 11th century, the Fifth Doctor, Adric, Nyssa and Tegan Jovanka took a trip to rural Eastern Europe and met a Tsar. (PROSE: The Immortals)
Peter the Great was titled the Tsar of All Russias. (AUDIO: Sound the Siren And I'll Come To You Comrade)
Nicholas I was the Tsar of Russia during the Crimean War in the 1850s. (AUDIO: The Angel of Scutari) In 1903, Nicholas II was the Tsar of Russia. (AUDIO: The Wanderer)