Ivan IV Vasilyevich (Russian: Ива́н Васи́льевич, tr. Ivan Vasilyevich; 3 September [O.S. 25 August] 1530 – 28 March [O.S. 18 March] 1584), commonly known as Ivan the Terrible or Ivan the Fearsome (Russian: Ива́н Гро́зный , Ivan Grozny, with correct translation from Russian being Ivan the Formidable), was the Grand Prince of Moscow from 1533 to 1547, then "Tsar of All the Russias" until his death in 1584. The last title was used by all his successors.

During his reign, Russia conquered the Khanates of Kazan, Astrakhan and Sibir, becoming a multiethnic and multicontinental state spanning approximately 4,050,000 km² (1,560,000 sq mi). Ivan exercised over Russia's hereditary nobility and developed a bureaucracy to administer his new territories. He transformed Russia from a medieval state into an empire, though at immense cost to its people, and its broader, long-term economy.

Historic sources present disparate accounts of Ivan's complex personality: he was described as intelligent and devout, yet given to rages and prone to episodic outbreaks of mental instability that increased with his age. In one such outburst, he killed his son and heir Ivan Ivanovich. This left his younger son, the pious but politically ineffectual Feodor Ivanovich, to inherit the throne.

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