At Wudang mountain and during the Song dynasty (960 – 1279), there would have lived a
Taoist hermit called Zhang San Feng.

It is said that on one occasion he watched a fight
between a snake and a magpie… “after a duel the magpie
was defeated by the snake; the latter had fought with
flexibility, moving with curved movements. Then Zhang
San Feng realized the supremacy of flexibility over
rigidity, the interchange of yin and yang, and other
concepts which are the foundation of Taiji Quan.
After this incident he developed Taiji Quan.”

Several authors of books on Taiji Quan believe
in this legend:

Xu Yusheng Taijiquan Tushi Jie, 1921.

Sun Lutang Taiji Quanxue, 1924.

Chen Weiming Taiji Quan Shu, 1925.

Yang Chengfu Taiji Quan Tiyong
Quanshu, 1934.

This is a controversial character from whom no precise information has been
gathered. A thorough explanation which even relates him to Jiang Fa, contemporary of
Chen Wang Ting, as well as possible historical documentation, can be found at :
http://www.literati-tradition.com/zhang_sanfeng_camp.html