In the history of Chinese calligraphy, there are two people known as: "Cao Sage", one is Zhang Zhi in the Later Han Dynasty, and the other is Zhang Xu in the Tang Dynasty. "Grass Saint" generally refers to Zhang Xu.
Zhang Zhi (alias Boying) of the Later Han Dynasty was a native of Jiuquan, Dunhuang. He is diligent in studying the past and is indifferent to official advancement. The imperial court said that Youdao could not be conquered, and people at that time respectfully called themselves "Zhang Youdao". Good calligraphy, best at cursive writing. Zhang Zhi once went to a pond to study calligraphy. The water in the pond was black, and he practiced calligraphy while wearing silk clothes at home. This shows the depth of his skills. He was praised by later generations as "unparalleled and unparalleled." He was respected as the "Grass Saint". Zhang Zhi has always enjoyed a very high status as a sage in the world of calligraphy. In the volume of "Shu Duan", Zhang's cursive script and cursive script are listed as divine products, saying: "You are particularly good at Zhang cursive script, and gave birth to Du Du and Cui Ai. The dragon and leopard changed, and the green came out of the blue. It was also created in Jincao. The sky is unique and expressive. "It's so vast that you don't regret anything. It's like a clear stream with a long source, flowing infinitely, lingering back to the cliff valley, letting nature take its turn." The grass methods of Zhang Xu, Wei Dan, Suo Jing, Wang Xizhi and his son, Zhang Xu, and Huai Su all originated from Boying. Yang Xinyun said: "Zhang Zhi, Huang Xiang, Zhong Yao, and Suo Jing were called "sages of calligraphy" at that time. However, Zhang was strong in bones and muscles, and ranked first among all sages in virtue. They are worthy of their place."
Zhang Xu (658-742), courtesy name Bogao, was a native of Wu County (now Suzhou, Jiangsu Province). During the Kaiyuan and Tianbao years of the Tang Dynasty, he traveled to Jingzhao (today's Xi'an) as an official. He first served as Changshu Wei and Guan Zuo, and led the governor of the government. He was known as "Zhang Changshi" in the world. Gongshu, named "Cao Sheng", during the reign of Emperor Xuanzong, Li Bai's poems, Pei Fang's sword dancing, and Zhang Xu's cursive script were regarded as the "three uniques". Li Qi's "Gift to Zhang Xu": "The top of the bed is exposed, and there are three or five long calls. When he is happy, he sprinkles the plain wall, and his pen is like a shooting star." Zhang Xu's handed down manuscripts include "Tie of Belly Pain", "Four Posts of Ancient Poems" ", and there is also the regular script "Lang Guan Ji", which proves that his "Bian" characters are not outrageous and have rules.