Which calligrapher's creative background is described in the poem "Take off your hat and show off the top of the princes"?

Zhang Xu is famous for his drinking. In Du Fu's poem "Song of Eight Immortals Drinking", Zhang Xu is also one of the characters described, and he is called "Eight Immortals Drinking" together with others. Zhang Xu is famous for his most unrestrained and free cursive script in calligraphy. According to New Tang Book, Zhang Xu likes to write after drinking, which is called "Crazy Grass". His calligraphy is mostly connected with grotesque shapes, exaggerated thickness contrast and emotional lines, and is praised as "endless changes, if God helps" by Old Tang Book [1]. However, Zhang Xu not only wrote cursive script, but also was the grandson of another famous calligrapher in Tang Dynasty, Lu Jianzhi. He was also proficient in regular script and Chinese painting. According to legend, his wild grass was inspired by watching others fight and practice swords. Before Zhang Xu, the calligraphy circle always took Wang Xizhi and Wang Xianzhi as the norms, but Zhang Xu's calligraphy broke this convention and brought a whirlwind change to the calligraphy circle. [Editor] The radical calligrapher [Editor] who has never been seen before said that Yan Zhenqing and Li were his disciples, but there is no evidence, so it is difficult to determine the authenticity. Yan Zhenqing later became a calligraphy reformer in the Tang Dynasty. There are many records about Zhang Xu in the Tang Dynasty. The most well-known is that he even wrote with his hair when he was inspired by drinking. Zhang Xu's handed down works include Four-character Poems, Thousand-character Works, Langguan Shizhu Ji, Sad Autumn Fu, Abdominal Pain Post and so on. Among them, Four Ancient Poems includes two poems by Yu Xin and two poems by Xie Lingyun: Ode to the Prince, Ode to the Husband under the Rock and Ode to a Four-or Five-year-old Boy, with a total of 40 lines. Height 28.8 cm, width 192.3 cm, written on five-color paper. It is now in the Liaoning Provincial Museum in China. His works have been loved by Tang Wenzong and Li Ang and listed as one of the "Three Musts".