Li Su () (773–821), courtesy name Yuanzhi (), formally Duke Wu of Liang (), was a Chinese military general and politician during the Tang Dynasty. He was most well—known for his surprise attack on Cai Prefecture (蔡州, in modern Zhumadian, Henan), then held by the warlord Wu Yuanji, successfully capturing Wu.
Background
Li Su was born in 773, during the reign of Emperor Daizong. His father was Li Sheng, who would later rise to prominence as a major general during the reign of Emperor Daizong's son Emperor Dezong. When Li Su was young, on account of his father's accomplishments, he was first made Xielü Lang (), a low-level official in charge of music at the ministry of worship (太常寺, Taichang Si), and later the deputy minister of army supplies (衛尉少卿, Weiwei Shaoqing). His birth mother died early, so he was raised by another concubine of Li Sheng's, Lady Wang, who was created the Lady of Jin. When Lady Wang died, Li Sheng, because she was not his wife, did not have Li Su observe the mourning rites for a mother, but Li Su tearfully requested to be allowed to observe those rituals, and Li Sheng agreed.
After Li Sheng died in 793, Li Su and his brother Li Xian () built a tent next to Li Sheng's tomb, intending to observe the mourning period there. Emperor Dezong, believing the conditions were too harsh, ordered them to return to their own mansion, but after they went home for one night, the next day they were at the tomb again, and Emperor Dezong allowed them to continue to observe the mourning period there. After the mourning period was over, Li Su was made a member of the staff of Li Song the Crown Prince. He later served successively as the prefect of Fang (坊州, in modern Yan'an, Shaanxi) and then Jin (晉州, in modern Linfen, Shanxi) Prefectures, and was given the honorary title Jinzi Guanglu Daifu () on account of his virtues. He later was recalled to again serve on the Crown Prince's staff, and later served as the head of the Crown Prince's household.
During Emperor Xianzong's reign
During the campaign against Wu Yuanji
It was said that Li Su was full of strategies and capable in horsemanship and archery. In 816, during the reign of Emperor Dezong's grandson Emperor Xianzong, imperial troops were conducting a campaign against the warlord Wu Yuanji, who controlled Zhangyi Circuit (彰義, headquartered in modern Zhumadian, Henan)) without imperial approval, two successive imperial generals put in command of nearby Tangsuideng Circuit (唐隨鄧, headquartered in modern Zhumadian) — Gao Xiayu () and Yuan Zi — had suffered defeats by Zhangyi troops. Li Su volunteered to serve in the campaign, and the chancellor Li Fengji also knew of Li Su's abilities, and therefore recommended him. Emperor Xianzong thus made Li Su the military governor (Jiedushi) of Tangsuideng Circuit, as well as the prefect of its capital Tang Prefecture (), replacing Yuan.
When Li Su reached the front in spring 817, it was said that the Tangsuideng soldiers, having suffered many defeats, were fearful of war. Li Su first comforted them by stating that his intentions were not to engage in battles immediately, and further personally attended to the wounded, to try to raise the morale. He also acted as if he was not taking military discipline seriously and not taking precautions toward Zhangyi troops, in order to get Zhangyi's guards down toward him. With Li Su not being well-known and the Zhangyi troops having just defeated Gao and Yuan, Zhangyi did not take particular precautions toward Li Su.