According to the "Records of the Grand Historian", written by Sima Qian during the Han dynasty, the first emperor was the eldest son of the Qin prince Yiren, who later became King Zhuangxiang of Qin. Prince Yiren at that time was residing at the court of Zhao, serving as a hostage to guarantee the armistice between the Qin and Zhao states. Prince Yiren had fallen in love at first sight with a concubine of Lü Buwei, a rich merchant from the State of Wey. Lü consented for her to be Yiren's wife, who then became known as Lady Zhao (Zhao Ji) after the state of Zhao. He was given the name Zhao Zheng, the name name Zheng () came from his month of birth "Zhengyue", the first month of the Chinese lunar calendar; the clan name of Zhao came from his father's lineage and was unrelated to either his mother's name or the location of his birth. (Song Zhong says that his birthday, significantly, was on the first day of Zhengyue.) Lü Buwei's machinations later helped Yiren become King Zhuangxiang of Qin in 250 BC.