Yi Yin 伊尹 "Governor Yi", personal name Yi Zhi 伊挚, Aheng 阿衡 or Baoheng 保衡 (Yin is traditionally explained as a courtesy name but rather seems to have been a title of official, something like "governor"; the same is true for the terms Aheng "adhering to balance" and Baoheng "protecting justice"), was a counsellor to the early kings of the Shang dynasty 商 (17th to 11th cent. BCE).
According to legend, Yi Yin was born as a slave in the household of Lord Nüteng 女媵 of Xin 莘. According to another, popular legend, the daughter of Lord Xin found him as a baby in his swaddling clothes when she plucked mulberry leaves and adopted him. Yi Yin grew up as a kitchen servant of Lord Xin. The mother of Yi Yin had transformed into a muberry tree when she was endangered by the floods of River Yi 伊水. This story is told in the book Lüshi chunqiu 呂氏春秋. The daughter of Lord Xin later married Tang the Perfect 成湯, and Yi Yin became a minor official (xiaochen 小臣) of Tang the Perfect.
Yi Yin's new master soon recognized the political talent of Yi Yin and made him his counsellor. Yi Yin suggested overthrowing the Xia dynasty 夏 (17th to 15th cent. BCE) and campaigning against the brutal King Jie 桀. When Tang was held prisoner by King Jie, Yi Yin bought his master free with the help of jewellery. When Tang was set free, Yi Yin planned the campaigns to conquer the territories of Ge 葛, Wei 韋, Gu 顧 and Kunwu 昆吾, and finally that against the Xia kingdom. When Tang founded the Shang kingdom, he appointed Yi Yin his counsellor-in-chief (aheng). Yi Yin established rules for the relation between the Shang court and the regional states that had to deliver tributes to the Shang.
After the death of King Tang, Yi Yin served the kings Bu Bing 卜丙 (or Wai Bing 外丙), Zhong Ren 中壬 and Tai Jia 太甲. He formally introduced to the late king the temple name Zhongzong 中宗. Yet King Tai Jia discarded the virtuous ways of rule established by his predecessors and did not care for a benevolent way of government. Yi Yin thereupon decided to arrest the king and put him under house arrest in Tong 桐. After three years Yi Yin, as a factual usurper, repented his exaggerated step and gave back the reins into the hands of King Tai Jia. After the death of Tai Jia, Yi Yin proclaimed the "Lessons from the Case of Tai Jia" (Tai Jia xun 太甲訓), that was originally a chapter of the Classic Shangshu 尚書 "Book of Documents", but unfortunately went lost.
Yi Yin died during the reign of King Wo Ding 沃丁 and was buried near the capital Bo 亳 in the manner of a king. Important sacrifices to Yi Yin are also mentioned in the oracle bone inscriptions of the Shang which demonstrates that he occupied a high position in the hierarchy of the Shang ancestors. According to some sources, the usurper Yi Yin was killed by King Tai Jia when the latter secretly returned from his exile in Tong.
There are several other names by which the person Yi Yin is called in Chinese historiography and literature, like Yizi 伊子 "Master Yi", Yi Bo 依伯 "Earl Yi", Yi Gong 依公 "Duke Yi", Qi Heng 猗衡, Tai A 太阿, Yuansheng 元聖 "Primordial Holy", Xiaochen 小臣 "Minor Official" or Xiaozi 小子 "Minor Baron".