Has there been anyone in history worse than Mao Zedong?

A lot. For example, Washington is worse than Mao. Washington made an alliance with the tyrant of Europe to annex the colony of then the most democratic country and built the last country of slavery in human history. Washington built a country of slavery that lasted nearly a century, followed by a century of racial segregation and lynching. Mao built a country without slavery and racial segregation.