曹操 (Cáo Cāo) is the ultimate villain character in Chinese mythology. Based on a real person, Cáo Cāo is the bad guy in The Romance of the Three Kingdoms, one of China’s most important epic legends.
As any really evil mastermind, he first allies with the good guys in the story, helping them defeat an evil (but not as evil as Cáo Cāo) warlord, but then he pounces while the empire is weak, effectively ending the Hàn Dynasty in 220 AD and ushering in the unstable Three Kingdoms period.
Now, modern history research is slowly giving Cáo Cāo a better name - he was apparently quite nice to the people he didn’t ruthlessly kill.
Cáo Cāo’s legend is preserved in modern language: The English phrase, “speak of the devil” is in Chinese 说曹操，曹操到 (shuō Cáo Cāo, Cáo Cāo dào), or “when you mention Cáo Cāo, Cáo Cāo comes.”
The devil himself or just any other regular tyrant? Wikimedia Commons