Ivan the Terrible

Ivan IV Vasilyevich, known in English as Ivan the Terrible was Grand Prince of Moscow from 1533 until his death. His long reign saw the conquest of the Khanates of Kazan, Astrakhan, and Siberia, transforming Russia into a multiethnic and multiconfessional state spanning almost one billion acres, approximately 4,046,856 km2 (1,562,500 sq mi). Ivan managed countless changes in the progression from a medieval nation state to an empire and emerging regional power, and became the first ruler to be crowned as Tsar of All Russia.

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 illness. One notable outburst may have resulted in the death of his groomed and chosen heir Ivan Ivanovich, which led to the passing of the Tsardom to the younger son: the weak and possibly mentally retarded Feodor I of Russia. His contemporaries called him "Ivan Groznyi" the name, which, although usually translated as "Terrible", actually means something closer to "Great" and carries connotations of might, power and strictness rather than horror or cruelty.

(From wikipedia)