Reign: 247-210 B.C.
Qin, also called Qin Shihuangdi, united China in 221 B.C. and ruled as the first emperor of the Qin dynasty. He was known to order the killing of scholars whose ideas he disagreed with and the burning of "critical" books.
During his reign, he ordered the construction of a great wall (roughly speaking, the prequel to the modern Great Wall of China), and an enormous mausoleum featuring more than 6,000 life-size terra-cotta soldier figures. Large numbers of conscripts working on the wall died, and those working on the mausoleum were killed to preserve the secrecy of the tomb.
"Every time he captured people from another country, he castrated them in order to mark them and made them into slaves," Hong Kong University's Xun Zhou told the BBC.
Source: British Museum, Britannica, History, BBC