The person related to the allusion of "Iron Threshold" is Zhiyong.
Zhiyong was a monk of Yongxin Temple in Xing Wu in Sui Dynasty. When he was young, he inherited the family tradition and studied Wang Xizhi's ancestral method. After becoming a monk, he studied calligraphy upstairs in Yongxin Temple for decades, and vowed that "if the book fails, he will not go downstairs". He is very diligent in learning calligraphy, and has written as many as 8 copies of Wang Xizhi's "True Grass Thousand Characters" alone. The bald pen written by him was replaced and put into the bamboo slips, and there were as many as five bamboo slips. So, he buried these bald pens in the ground and piled them into graves, and personally wrote the words "returning the pen grave" as a souvenir.
after his fame was greatly boosted, people who asked for calligraphy came in droves, and the temple's threshold was trampled down. So, I had to wrap the threshold with iron. Since then, this famous "iron threshold" allusion has been left in the history of calligraphy.
character evaluation
There are many comments on Zhiyong's calligraphy by calligraphers and calligraphy works in past dynasties. Xue Shiyun of Le 'an said, "Zhi Yong is a master of calligraphy between Sui and Tang Dynasties." Du Mu's "Implication Compilation" says: "Zhi Yong is a true grass with thousands of original works, and his charm is flying, and he is superior to the gods, ranking first in the world." Xie Jinyun: "Zhiyong Yaotai Snow Crane, mark the group high." Wei Xu's "On Nine Scholars" says: "Wisdom is always the grass, and the quality is below."