The Mizi 宓子 "Master Mi", also written 密子 or Lüzi 慮子, and also read Fuzi, is a Confucian treatise written by the Warring States period 戰國 philosopher Mi Buqi 宓不齊 (521-? BCE), courtesy name Mi Zijian 宓子賤, from the state of Lu 魯. He was a disciple of Confucius and once occupied the post of counsellor (zai 宰) of the statelet of Shanfu 單父 (modern Shanxian 單縣, Shandong). In this position, he reigned with the help of ritual music and always cared for the welfare of the town of Shanfu. He also appointed competent and wise ministers in the offices of Shanfu. According to the imperial bibliography Yiwenzhi 藝文志 in the official dynastic history Hanshu 漢書, the Mizi was 16 chapters long. The text was lost at an early point of time, but the Qing period 清 (1644-1911) scholar Ma Guohan 馬國翰 collected surviving fragments quoted in the books Hanfeizi 韓非子, Lüshi chunqiu 呂氏春秋, Huainanzi 淮南子, Shuoyuan 說苑 and Kongzi jiayu 孔子家語 and published these in his reprint series Yuhan shanfang yiji shu 玉函山房輯佚書. The Mizi says that human nature is both good and evil. A similar book to the Mizi was the Jingzi 景子, written by a disciple of Mi Buqi.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, vol. 2, p. 1543. Changchun: Jilin daxue chubanshe.