There are many contenders for the title of most dangerous man in history. Adolf Hitler, Joseph Stalin, and Genghis Khan were all responsible for the deaths of millions of people. However, if we consider the criteria of who caused the most death and destruction, then the clear winner is Mao Zedong.
Mao was the founder of communist China and ruled from 1949 until his death in 1976. During his reign, he implemented a series of disastrous policies that led to widespread famine and death. The Great Leap Forward was an attempt to increase agricultural production through forced collectivization and industrialization. This resulted in mass starvation as food was taken from farmers to be used for industry instead. It is estimated that between 15 and 45 million people died as a result of this policy.
The Cultural Revolution was another disastrous policy implemented by Mao that led to more death and destruction. This policy aimed to eliminate all traces of capitalism and traditional culture from China. It resulted in widespread violence as well as economic ruin. An estimated 1-2 million people were killed during this time period, making it one of the deadliest episodes in human history