Eunuch: A man whose external genitalia have been surgically removed so that he can work as a harem attendant or other court functionary. In some cultures, only the testicles would be removed, while in others, the penis was cut off as well.
Common in Imperial China; also prevalent in the courts of Sumeria, Assyria, Egypt, Persia, and Anatolia (Turkey).
The word eunuch comes from the Greek eune "bed" and ekhein "to keep," so "bed-keeper." This reflects a primary function of many eunuchs, protecting a king's wives and concubines.
"The famous Hui Chinese admiral and explorer, Zheng He, was a eunuch."