The Oprichniks were members of his private army, which he used to terrorize the boyars, and the first Zemsky Sobor was called by him.
This ruler had military success in taking Dorpat, and inaugurated an eastward expansion after conquering Astrakhan. He celebrated another victory by having Barma construct a religious structure also known as the Cathedral of Intercession of the Virgin on the Moat. However, he gave up Narva in the Treaty of Plussa with Sweden, and in the Treaty of Jam Zapolski, renounced claims to Livonia. The Oprichniks were members of his private army, which he used to terrorize the boyars, and the first Zemsky Sobor was called by him. His son Feodor was succeeded by Boris Godunov, who likely killed his youngest son Dmitri. FTP, name first Russian to take the title of tsar, who was nicknamed for his fearsome acts.
This ruler had military success in taking Dorpat, and inaugurated an eastward expansion after conquering Astrakhan.
Ivan IV or Ivan the Terrible or Ivan Groznyi