Josef Stalin: He is directly linked to the death of almost 12 million persons (non-combat), compared to the accepted figure of 6 million for Hitler's Holocaust.
His actions in the early 1930's led to famine in the Ukraine that is estimated to have killed 6 to 7 million.
Prior to the war he ordered "The Great Purge" in the Soviet Union. During 1937 and 1938, the NKVD (predecessor to KGB) detained 1,548,367 victims, of whom 681,692 were shot - an average of 1,000 executions a day. The best estimate of deaths brought about by Soviet Repression during these two years is the range 950,000 to 1.2 million, which includes deaths in detention and those who died shortly after being released from the Gulag as a result of their treatment in it.
On March 5, 1940, the Soviet leadership approved an order of execution for more than 25,700 Polish "nationalist, educators and counterrevolutionary" activists in the parts of the Ukraine and Belarus republics that had been annexed from Poland. This event has become known as the Katyn Massacre.
Stalin feared that Hitler would use disgruntled Soviet citizens to fight his regime, particularly people imprisoned in the Gulags. He thus ordered the NKVD to take care of the situation. They responded by murdering around one hundred thousand political prisoners throughout the western parts of the Soviet Union, with methods that included bayoneting people to death and tossing grenades into crowded cells.
According to recent figures, of an estimated four million POWs taken by the Russians, including Germans, Japanese, Hungarians, Romanians and others, some 580,000 never returned, presumably victims of privation or the Gulags