Zheng Zhong (鄭眾), courtesy name Jichan (季產) (died 107), was the first Han Dynasty eunuch with true power in government, thanks to the trust that Emperor He had in him for his contributions in overthrowing the clan of Empress Dowager Dou, particularly her autocratic brother Dou Xian. He was also a close associate of Emperor He's wife Empress Deng Sui and continued to be powerful after Emperor He's death, during her regency over his son Emperor Shang and Emperor An. He was also the first Eastern Han Dynasty eunuch to be created a marquess. (The only Western Han Dynasty eunuch who was created a marquess was Empress Xu Pingjun's father Xu Guanghan (許廣漢), whose creation was thanks to his relationship with his daughter and his son-in-law Emperor Xuan, not his post as a eunuch.)
Zheng was from Nanyang Commandery (roughly modern Nanyang, Henan) -- the same commandery that the Eastern Han imperial clan was from. He was described to be cautious, agile, and a deep thinker. He first served in the household of Emperor Zhang while he was still crown prince under his father Emperor Ming. After Emperor Zhang ascended the throne, he was eventually promoted to the post of imperial attendant (中常侍).
During the time of Empress Dowager Dou's regency over Emperor He, Zheng served as the director of imperial gardens (鉤盾令). He was one of the eunuchs who did not endear himself to Empress Dowager Dou's clan. In 92, Emperor He, apparently dissatisfied with his suppression by the Dou clan, plotted a coup d'état with his brother Liu Qing the Prince of Qinghe, and Zheng. They were successful in carrying out the overthrow of the Dous, and as a reward, Emperor He promoted Zheng to the post of the empress' palace's head of household (大長秋). Zheng accepted the post but declined most of the monetary rewards that Emperor He gave him, a fact that made Emperor He even more impressed with him. Emperor He often consulted with him on major affairs of state, and this started a precedent of eunuchs becoming involved in imperial governance.
In 102, breaking past precedent, Emperor He created Zheng the Marquess of Chaoxiang.
Zheng supported Emperor He's wife Empress Deng through the turmoils of Emperor He's death in 106 and the death of his son and successor Emperor Shang later that year. For his support, she added 300 households to his march in 107. He died later that year.