Stalin alone:

https://en.wikipedia.org/wiki/Joseph_Stalin

Conversely, his totalitarian government has been widely condemned for overseeing mass repressions, ethnic cleansing, executions, and famines which caused the deaths of millions.

https://en.wikipedia.org/wiki/Excess_mortality_in_the_Soviet_Union_under_Joseph_Stalin

This contained official records of 799,455 executions (1921–1953),[8] around 1.7 million deaths in the Gulag,[9][10] some 390,000[11] deaths during the dekulakization forced resettlement, and up to 400,000 deaths of persons deported during the 1940s,[12] with a total of about 3.3 million officially recorded victims in these categories.[13] According to historian Stephen Wheatcroft, approximately 1 million of these deaths were "purposive" while the rest happened through neglect and irresponsibility.[2] The deaths of at least 5.5 to 6.5 million[14] persons in the Soviet famine of 1932–1933 are sometimes, though not always, included with the victims of the Stalin era.[2][15]