Yiren was born to Lord Anguo, the second son and heir apparent of King Zhaoxiang, and Lord Anguo's concubine Lady Xia. He was chosen to serve as a hostage in the Kingdom of Zhao. In Handan (the capital of Zhao) he met a merchant, Lü Buwei, who saw Yiren as extraordinary and detected in him the potential to become the king of Qin in the future. Lü Buwei treated Yiren well and presented his concubine Lady Zhao to Yiren. Lady Zhao later bore Yiren a son, Ying Zheng.
In the meantime, through bribes and machinations, Lü Buwei helped Yiren return to Qin. He also successfully persuaded Lord Anguo's primary spouse, the childless Lady Huayang, to adopt Yiren as her own son, thereby making Yiren become Lord Anguo's legitimate heir apparent. As Lady Huayang was a native of the Chu state, she renamed Yiren to "Zichu" (lit. "son of Chu"). Upon the death of King Zhaoxiang in 251 BC, Lord Anguo ascended the throne and became historically known as "King Xiaowen", but he died in the following year just three days after his coronation. Zichu succeeded his father as the king of Qin and became historically known as "King Zhuangxiang of Qin". He named Lü Buwei as his chancellor, Lady Zhao as his queen consort, and Ying Zheng as his crown prince.
King Zhuangxiang died in 247 after reigning for three years. Ying Zheng succeeded him and eventually unified China through a series of wars against the other six major states, established the Qin Dynasty in 221 BC, and became historically known as "Qin Shi Huang" (First Emperor of Qin).