Yermak Timofeyevich explored Siberia in the name of this ruler.
Yermak Timofeyevich explored Siberia in the name of this ruler. This ruler conquered Kazan and Astrakhan but was defeated by Stephen Batory and Sigismund II in the Livonian War. He abdicated his throne to Simeon Bekbulatovich for a year. This ruler organized the streltsy, suppressed the power of aristocratic families with his oprichnina, and called the first "assembly of the land," or (*) zemsky-sobor. This Rurik ruler accidentally killed his chosen heir, which forced him to appoint the mentally disabled Feodor I as his successor instead. For ten points, identify this first Russian tsar who was known for his extreme cruelty.
Yermak Timofeyevich explored Siberia in the name of this ruler.
{Ivan the Terrible} (or {Ivan IV}; or {Ivan Grozny}; or {Ivan Vasilyevich}; prompt on “Ivan”)