I have an old Guiness Book of World Records which lists that Stalin murdered 35 million.
They list Chairman Mao as the most prolific murderer in history. His number was 60 million.
These figures do not include war casualties.
I have no idea how they arrived at those figures.
Neither do I. They are all roundabout estimates. Kurganov's seems the only reliable approach, but it cannot distinguish direct murder from artificial famine or unnecessary wars, or casualties contrary to any military sense even in a defensive war.
And then there’s Rachel Carson - 50 million and counting.