From:
http://www.taipeitimes.com/news/2000/05/25/story/0000037415 "Two new biographies of Mao have recently been published. One is Mao Zedong by the well-known scholar and author Jonathan Spence; the other is Mao: A Life by British journalist Philip Short....
Both express their shock over the massive scale of turbulence incited by Mao. According to a figure quoted by Mao in Spence's book,
about 700,000 landlords and counter-revolutionaries were killed in the "land reform movement" between 1950 to 1952. During the "Great Leap Forward" of 1960 and 1961, 20 million people died of starvation.
According to Spence, millions more died in the Cultural Revolution, while Short estimates the death toll at about 23 to 35 million.Short concludes that Mao caused more deaths than any other political leader in world history. He says the sins of Mao were even graver than those of Stalin and Hitler."
Going to have to go some to top that, I think.