Which czar used secret police to maintain strict control over the people?

As a citizen of Muscovy, you would have feared Czar Ivan IV, who ruled during the 1500s. Known as "Ivan the Terrible," he used a secret police force to tighten his iron grip on the people and control their lives. Known as "Ivan the Terrible," Ivan IV used a secret police force to tighten his iron grip on the people and control their lives.