Which Russian ruler was nicknamed "the Terrible"?

Ivan the Terrible was the first tsar of all Russia. During his reign, he acquired vast amounts of land through ruthless means, creating a centrally controlled government. The grandson of Ivan the Great, Ivan the Terrible, or Ivan IV, acquired vast amounts of land during his long reign (1533-1584), an era marked by the conquest of the khanates of Kazan, Astrakhan, and Siberia. Ivan the Terrible created a centrally controlled Russian state, imposed by military dominance. Many believe him to have been mentally ill. One of his violent outbursts was perhaps the reason for his son's death.

Source: The Westport Library