Weizi 微子, personal name Qi 啓, was an older half-brother of the bad last king of the Shang dynasty 商 (17th to 11th cent. BCE), King Zhou 紂. Wei 微 was the name of his fief near the capital of the Shang.
Weizi often remonstrated against the evil conduct of government and finally left the court. When King Wu 周武王 of the Zhou 周 (11th. cent.-221 BCE) conquered the Shang kingdom, Weizi submitted, offering to take over the responsibility for his brother's misdoings. After the last rebellious prince of the Shang, Wu Geng 武庚, was defeated, King Wu of Zhou enfeoffed Weizi with the territory of Song 宋. The charge of the enfeoffement was written down in the chapter Weizi zhi ming 微子之命 of the Classic Shangshu 尚書.