What was Ivan the Terrible greatest accomplishments during his rein.?

Ivan the Terrible, the first Tsar of Russia, is known for several significant accomplishments during his reign. He expanded the Russian territory dramatically, notably through the conquest of Kazan and Astrakhan, which opened up trade routes and increased access to the Volga River. Ivan also implemented a centralized administrative system, strengthened the power of the monarchy, and established a formalized legal code. Additionally, he was a patron of the arts and culture, most famously commissioning the construction of St. Basil's Cathedral in Moscow.