Lei Zhenzi and Yunzhongzi

Yunzhongzi saw the infant Ji Chang had found after the thunderstorm on Mount Yan, told the Earl of the West that the child was destined to be his disciple, and carried him back to the Yuzhu Cave on Mount Zhongnan under the name Lei Zhenzi. For seven years Yunzhongzi taught him the Golden Staff and how to read wind and thunder, and never let him come down.

When Ji Chang fled Chaoge and was blocked outside Lintong Pass by pursuers, Yunzhongzi sent his disciple to a mountain stream for a weapon. Lei Zhenzi ate two immortal apricots beside it and returned to the cave with an indigo face, fangs and wings on his back. Yunzhongzi taught him the use of the wind-and-thunder wings and told him only to save his father and not to kill for the sake of killing.

Having escorted Ji Chang back to Western Qi, Lei Zhenzi returned to the cave as ordered. Late in the Investiture war Yunzhongzi sent him down again, and from then he carried the staff with the Zhou army all the way to Chaoge.