Jizi 箕子, personal name Xu Yu 胥余, was an uncle of the bad last ruler of the Shang dynasty 商 (17th to 11th cent. BCE), King Zhou 紂, and occupied the position of Grand Preceptor (taishi 太師). Ji 箕 was the name of his fief.
When King Zhou was drinking day and night and lost awareness of time, Jizi was one of the few persons conscious of the coming downfall of the kingdom, yet he did not dare to criticize his nephew out of fear for his life. Asked for the daytime, he therefore pretended not to know it.
Yet Jizi is also known as a very upright minister who frequently remonstrated against King Zhou's conduct of government. In the book Hanfeizi 韓非子, his critique towards the king's use of ivory chopsticks is mentioned. After King Zhou had his upright minister Bi Gan 比干 killed, Jizi feigned to be mad in order to escape disaster, but he was encarcerated.
When King Wu 周武王 of the Zhou 周 (11th. cent.-221 BCE) conquered the Shang kingdom, Jizi was enfeoffed and became a subject of the Zhou. He is said to have been the author of the cosmological chapter Hongfan 洪範 in the Classic Shangshu 尚書.
From the Han period 漢 (206 BCE-220 CE) on, Jizi is said to have migrated to Korea (Chosŏn 朝鮮), where he introduced agriculture and so became the cultural hero Gija. His transfer to the Korea is described in the Shangshu dazhuan 尚書大傳.