Cao Cao
Cao Cao, or Cao Mengde, was generally considered a villain in the Three Kingdoms period. He was originally an official in the government but lost his post and became a fugitive when he failed to assasinate the tyrant Dong Zhuo.
After escaping barely from the claws of Dong Zhuo, he worked with many people, including Liu Bei. After he was able to build up some followers, he tried to get rid of his strongest rival at the time, Yuan Shao. This was later known as the famous Battle of Guandu, in which Cao Cao defeated the Yuan army when the Yuan army outnumbered his greatly.
After defeating Yuan Shao, Cao Cao established the kingdom of Wei. Around this time, Shu and Wu were also established. Cao Cao tried to ally with the kingdom of Wu, which was currently ruled by Sun Quan, in an attempt to get rid of Liu Bei once for all. But, Wu refused. Cao Cao, furious over Wu's refusal, wanted to sweep Shu and Wu together. Shu's prime minister and the famous strategist, Zhuge Liang pursuaded Wu to ally with Shu in defence against the coming Wei. The final decisive battle took at Chibi, later to be known as the famous Battle of Chibi. Cao Cao lost horribly and almost got killed on the way back.
Soon after, the alliance of Shu and Wei was broken and Guan Yu was murdered by Wei soldiers. It was said that Wu, wanting to bribe Cao Cao, sent Guan's head to him because Cao Cao really liked Guan when he was alive. But when the box opened and Cao Cao asked Guan whether he was ok in a sarcastic voice, Guan suddenly opened his eyes. From around this time, Cao Cao started to feel a terrible headache. The famous doctor, Hua Tuo came to take a look and said that he would have to open up his head and take out the tumour inside. But being suspicious as he was, Cao Cao refused and imprisoned Hua Tuo. Hua Tuo later was murdered inside the prison and Cao Cao soon died.