Answer:
The Russian leader who came to power at the age of three and earned the nickname "the Terrible" was Ivan IV, also known as Ivan the Terrible. He ruled as the Grand Prince of Moscow from 1547 until his death in 1584. Ivan is remembered for several things, including his military conquests, his establishment of the Oprichnina (a secret police force that he used to eliminate his political enemies), and his brutal treatment of his own son and heir, which may have contributed to the downfall of the Rurik dynasty. Despite his many accomplishments, Ivan's legacy is a complicated one, and his reign is often seen as a mix of both progress and brutality.