Identifying the individual or group responsible for causing the most human deaths in history is a challenging task, as several historical figures have been associated with significant loss of life. Nonetheless, based on recorded events, the following are some of the individuals and groups who have been responsible for causing the most significant amount of deaths in history.

The first on the list is Mao Zedong, who was the head of the Communist Party of China and the founder of the People’s Republic of China. During his reign from 1949 to 1976, Mao’s policies caused the demise of millions of people. The Great Leap Forward, which triggered famine and resulted in the deaths of approximately 45 million people, and the Cultural Revolution, which caused the death of approximately 1.5 million people, were some of his notorious policies.
Joseph Stalin, the leader of the Soviet Union from 1922 until his death in 1953, implemented various policies responsible for the death of millions of people. Collectivization, which resulted in famine and the death of approximately 5 to 7 million people, and the Great Purge, which led to the demise of approximately 700,000 to 1.5 million people, were among his policies.
Adolf Hitler, the leader of Nazi Germany from 1933 to 1945, was responsible for millions of deaths during his reign. The Holocaust resulted in the deaths of approximately 6 million Jews, and millions of other individuals, including Romani people, disabled individuals, and political dissidents, were systematically murdered.
Genghis Khan, the founder and first emperor of the Mongol Empire, led brutal conquests that resulted in the demise of approximately 40 million people during his reign from the early 13th century to the mid-14th century.
Timur, also known as Tamerlane, conquered many territories during his reign in the 14th century, resulting in the deaths of approximately 17 million people in Central Asia and the Middle East.
European colonial powers caused the deaths of millions of people as a result of their imperialist policies and actions. The death toll associated with these policies, including slavery, forced labor, forced relocation, and the exploitation of natural resources, is believed to be in the millions.
Attila the Hun, who ruled the Hunnic Empire in the 5th century, led campaigns of conquest throughout Europe, resulting in the deaths of approximately 1.5 million people.
It is crucial to remember that the individuals and groups mentioned above were responsible for causing significant death and destruction. However, several historical figures and events are also associated with significant loss of life. Additionally, the estimated death tolls associated with these individuals and events may vary depending on the source.
In conclusion, it is challenging to identify the individual or group responsible for causing the most human deaths in history. However, based on recorded events, Mao Zedong, Joseph Stalin, Adolf Hitler, Genghis Khan, Timur, and European colonial powers are among those who have caused the most significant loss of life in history.