Zhao Gao 趙高 (died end of October 207 BC) was the chief eunuch during the Qin Dynasty of China, who played an instrumental role in the downfall of the Qin Dynasty. Note that although he is referred to as a eunuch, he was not castrated - he was born with a sexual disability.

During the reign of the First Emperor, Qin Shi Huang, Zhao was involved in the death of Marshal Meng Tian and his younger brother Meng Yi at the death of Qin Si Huang when Meng Tian was stationed at the northern border commanding more than 100,000 troops for the inconclusive Huns campaign. Meng was a reputable general and a faithful supporter of Fusu, the first son of Qin Shi Huang.

When Zhao was a minor official, he committed a crime punishable by death. Meng Yi was the official in charge of sentencing and he sentenced Zhao to death and removed him from the officials list as instructed by Qin Shi Huang. Zhao was later pardoned by Qin Shi Huang and returned to official status when the emperor recalled him to be a man good at his post.

After the sudden death of Qin Shi Huang at Shaqiu prefecture, Zhao and the Imperial Secretariat Li Si presuaded the emperor's second son Huhai to falsify the emperor's will. The fake decree forced Fusu to commit suicide and stripped the command of troops from Meng Tian. Due to the previous sentencing by Meng Yi, Zhao hated the Meng brothers and using the hands of Huhai, now the Second Emperor, he forced Meng Tian to commit suicide and killed Meng Yi.

Zhao Gao soon outmaneuvered Li Si. He let Li Si go through "The Five Pains" which were indeed Li's invention, these consisted of having the victim's nose cut up, cutting of a hand and a foot, then the victim was castrated and finally cut in half in line with the waist. He also executed Li Si's family down to the third generation.

In 207 BC, there were rebels all over China. Zhao was afraid that the Second Emperor might make him responsible for the uprisings. To pre-empt this Zhao forced the emperor to commit suicide and replaced him by Fusu's son, Ziying.

Ziying soon killed Zhao and surrendered to Liu Bang. The Qin Dynasty collapsed, three years after the death of Qin Shi Huang, and less than twenty years after it was founded.