He had a violent and unpredictable nature, but his nickname (Russian, grozny) is better translated as “awe-inspiring” rather than “Terrible”. From 1547 to 1563 he pushed through a series of legal and administrative reforms. He also continued to expand Russian territory although his campaigns against the Mongols and in Siberia were more successful than those in the west. In 1564 he entered on a reign of terror, caused partly by his deteriorating mental condition, and partly by his determination to wrest power from the boyars. He used a special body of civil servants, the oprichniki, to break the power of the nobility. Shortly before his death, he precipitated further turmoil for Russia by killing in a fit of rage his gifted son and heir, Ivan: although another son, Fyodor, succeeded him, power soon fell into the hands of his favourite, Boris Godunov.