Who is the Guangchengzi 广成子

Guangchengzi is a disciple of Yuanshi Tianzun in Yuxu Palace and one of the "Twelve Golden Immortals" of the Chan School. According to Shenxian Zhuan (Biographies of Immortals), Guangchengzi lived during the time of Xuanyuan (the Yellow Emperor). He resided in a stone chamber on Kongtong Mountain. The Yellow Emperor once came to him to ask about "the essence of the supreme Dao". Guangchengzi did not answer at first. Three months later, when the Yellow Emperor came again to inquire about "the way to cultivate one's body", Guangchengzi told him:

"The essence of the supreme Dao is profound and indistinct. Do not see, do not hear; hold your spirit in tranquility. Your body will naturally become upright. You must be pure and clear. Do not overwork your body, do not disturb your essence, and then you can attain longevity. Be cautious to guard the inner and block the outer; excessive knowledge leads to failure. I abide by the unity and dwell in harmony, so for twelve hundred years, my form has never decayed. Those who attain my Dao will become emperors; those who lose my Dao will remain as commoners. I am about to leave you, entering the boundless realm, roaming the limitless wilderness, sharing the brilliance of the sun and moon, and enduring as long as heaven and earth. All people will eventually die, but I alone shall exist."

After saying this, he imparted to the Yellow Emperor a scroll of Ziran Jing (The Scripture of Nature).