Who are the four great calligraphers in the Northern Song Dynasty?

Mi Fei, Huang tingjian, su Shi, and Cai Xiang. Su Shi (137-111), born in Meishan, Sichuan Province, was known as Zizhan and Dongpo Jushi. A famous writer, painter and calligrapher in the Northern Song Dynasty. Poetry is one of the eight great poets in Tang and Song Dynasties. He, his father, Su Xun, and his younger brother, Su Zhe, are well-known in the world for their poems, and the world is called "Sansu". Huang Tingjian (145 -115) was named Lu Zhi, a Taoist in the Valley. Later generations called him Huang Valley, later named Fu Weng, and Hongzhou Fenning (now Xiushui, Jiangxi). Poet and calligrapher of Northern Song Dynasty. In the fourth year of Yingzong Zhiping (167), he was a scholar. In 17, Wang Anshi was the prime minister, and the implementation of the new law was fiercely opposed by conservatives headed by Sima Guang. Later, the struggle between the old and new parties intensified until the demise of the Northern Song Dynasty. In this struggle, Huang Tingjian stood on the side of the old party. Although he did not take an active part in this struggle, he has been involved in the vortex of struggle all his life. Mi Fei (151-117) has the character stamp, with the number of Xiangyang Manshi, Haiyue Waishi and Lumen Jushi. Originally from Taiyuan, Shanxi, he settled in Zhenjiang, Jiangsu. He is called "Mi Dian" because of his eccentric personality and crazy behavior, and he is called "brother" when he meets a stone. Huizong Zhao was a doctor of calligraphy and painting, and was called "Mi Nan Guan". Mi Fei is good at poetry and prose, good at calligraphy and painting, and accurate in identification. He is a painter, appraiser and collector, and he is second to none among the "four calligraphers of Song Dynasty". His writing style is bold and unrestrained, and he is strict with statutes. "Biography of the History of the Song Dynasty and Wenyuan" said: "I am particularly wonderful in calligraphy, and I am fascinated by flying, and I have Wang Xianzhi's brushwork. Cai Xiang (112-167) was born in Jun Mo and Xinghua (now Xianyou, Fujian). In the eighth year of Tiansheng (13), he was a scholar, and successively served as a collator of Guan Ge, an admonisher's court, a historian's museum, an intellectual patent, a bachelor's degree in Longtuge, a bachelor's degree in Privy Council, a bachelor's degree in Hanlin, a third secretary, and a bachelor's degree in Duanming Temple in the Central Government of the Song Dynasty, and served as a transshipment ambassador for Fujian Road (now Fuzhou, Fujian), knowing Quanzhou, Fuzhou and Kaifeng (now Kaifeng, Henan) He gave the assistant minister of the Ministry of Rites a gift of "loyalty". Cai Xiang is honest, truthful, faithful and knowledgeable. In the history of calligraphy, there are four great calligraphers, Su, Huang, Mi and Cai, who are regarded as typical representatives of the calligraphy style in the Song Dynasty.