Bian Xiu the Concubine, AD 1127 Song Dynasty China

Lady Bian Xiu was no ordinary woman, she was the favourite of Emperor Qinzong but also one of the most devious and mentally disturbed. She plotted to kill the emperor's heir, as well as the chief consort while at the same time, conspired with the Jurchen of Jin Dynasty to topple down the Song Dynasty. 

She had an unpleasant taste and thirst for sadistic pleasure, gained by kidnapping orphans and refugees from the war and used them for her target practice on archery or simply something to test her blade with. When that wasn't enough, she would gather a group of captives, dressed them in jurchen clothing and slaughtered them so that she could gain recognition for her service. 

When the Jin invaded and sacked Bianjing, she made it sure that the army and defense was in chaos, so that the Jurchen could overcome the castle easily. After its fall, she represented herself to the Jurchen as an ally. However, despite what she did, the generals were suspicious about her intention and ordered her capture. Later, to the Jurchen's horror, they discovered the massacres and murders done in the name of Lady Bian and without hesitation, the Jin beheaded her and left the body to rot. 

It was chronicled that before she was about to be executed, she mentioned the following phrase:

"Do you think that barbarians like you are better than me? If I had known that my fate would end here, I would have killed the emperors and their families long back while you were still tending your horses. Neither of you, the Hans nor the Jurchen, deserve to rule this land! You will all die by the hands of those savages, more brutal than you are  "

Her threat meant nothing to the Jurchen at that time, but they would soon learn of their fate just less than a decade later, when the Mongol came and destroyed their empire.