Xǔ Xùn 許遜 (trad. 239–374), zì Jìng zhī 敬之, honoured as Xǔ zhēn jūn 許眞君 or Xǔ tiān shī 許天師, was the Eastern-Jìn Daoist alchemist and exorcist revered as the founding patriarch of the Jìng míng zhōng xiào dào 淨明忠孝道 (“Way of Pure Illumination, Loyalty, and Filiality”) centered at Xī shān 西山 (Nánchāng, Jiāngxī). His cult exploded in the SòngYuán era, with pseudepigraphic alchemical and ritual literature attributed to him — including KR5c0351 Xǔ zhēn jūn shí hán jì 許眞君石函記 (“Record of Perfected Xǔ’s Stone Casket”). Traditional lifedates 239–374 are hagiographic; the historical figure is obscured behind centuries of cult legend.