1. Cai Lun
2. Agha Mohammad Khan Qajar
After founding the Qajar dynasty of Iran, Agha Mohammad Khan Qajar ruled the dynasty from 1789 to 1797. He was popularly known as the eunuch Monarch as he was castrated during his younger days after getting captured by Adel Shah Afshar.
Farinelli was one of the most celebrated castrato singers and one of the greatest in the history of opera. Castrato, a male singing voice, is achieved by the castration of the singer before the singer hits puberty.
4. Sima Qian
Sima Qian is regarded as the father of Chinese historiography. He was castrated and sent to prison for defending a military officer named Li Ling. Upon his release, Sima chose to serve as a palace eunuch.
Bagoas was one of the most prominent and popular eunuchs as he served as Artaxerxes III's chief minister in the famous Achaemenid Empire. He served in this position until his death.