Mao Zedong
"On 1 October 1949, Mao proclaimed the foundation of the PRC, a Marxist–Leninist single-party state controlled by the CCP. In the following years he solidified his control through the land reform campaign against landlords, the Campaign to Suppress Counterrevolutionaries, the "Three-anti and Five-anti Campaigns", and through a truce in the Korean War, which altogether resulted in the deaths of several million Chinese. From 1953 to 1958, Mao played an important role in enforcing command economy in China, constructing the first Constitution of the PRC, launching an industrialisation program, and initiating military projects such as the "Two Bombs, One Satellite" project and Project 523. His foreign policies during this time were dominated by the Sino-Soviet split which drove a wedge between China and the Soviet Union. In 1955, Mao launched the Sufan movement, and in 1957 he launched the Anti-Rightist Campaign, in which at least 550,000 people, mostly intellectuals and dissidents, were persecuted. In 1958, he launched the Great Leap Forward that aimed to rapidly transform China's economy from agrarian to industrial, which led to the Great Chinese Famine and the deaths of 15–55 million people between 1958 and 1962."1
"Mao's policies were responsible for vast numbers of deaths, with estimates ranging from 40 to 80 million victims due to starvation, persecution, prison labour, and mass executions, and his government was described as totalitarian."1
Wikipedia's views on Mao, like other communists, is more mild than other sources. Some estimates of the deaths attributable to Moa soar past 100 million. I encourage you to read his bio and the links to the events he caused. But remember, he didn't personally kill many. He had regular people do the dirty work, most of them zealously.
1 & 2: https://en.wikipedia.org/wiki/Mao_Zedong
https://en.wikipedia.org/wiki/Maoism
https://en.wikipedia.org/wiki/Cultural_Revolution
https://en.wikipedia.org/wiki/List_of_massacres_in_China
https://www.mirror.co.uk/news/world-news/torture-mass-murder-rape-cannibalism-8017041