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Boris Godunov, a brother-in-law to Tsar Feodor, effectively ruled Russia as regent during Feodor's reign from 1584 to 1598. He was an influential and powerful figure in the government, wielding considerable control over state affairs. Known for his administrative skills and political acumen, Godunov played a pivotal role in managing the country's internal and foreign policies, leaving a lasting impact on Russia's development during that period.