Hou Junji (died April 29, 643) was a Chinese general and official who served as a chancellor during the reign of Emperor Taizong in the Tang dynasty. He is best known for leading the Tang military campaigns against the Gaochang and Tuyuhun kingdoms. In 643, he was implicated in a plot by the crown prince, Li Chengqian, to overthrow Emperor Taizong, and was executed.
During Emperor Gaozu's reign
Hou Junji's date of birth is unknown. Little is known about his family background other than that he was from Bin Prefecture (豳州, roughly modern Xianyang, Shaanxi). It was said that he was pretentious and always wanted to appear impressive. He favored using the bow and arrow; while he never achieved greatness in archery, he became known for his fighting abilities. At a point early in the reign of Emperor Gaozu, who was then still trying to reunify China after the collapse of the Sui Dynasty, Hou came to serve under Emperor Gaozu's son, the major general Li Shimin the Prince of Qin. While serving under Li Shimin, for his accomplishments, Hou was created the Viscount of Quanjiao. He also became a close associate of Li Shimin, often offering Li his strategies.
By 626, Li Shimin was locked in an intense rivalry with his older brother Li Jiancheng, who was the Crown Prince. He feared that Li Jiancheng would kill him. Hou, along with Li Shimin's brother-in-law Zhangsun Wuji, Zhangsun's uncle Gao Shilian, and the general Yuchi Gong, advised Li Shimin to act first and ambush Li Jiancheng and another brother who supported Li Jiancheng, Li Yuanji the Prince of Qi. Li Shimin agreed, and in 626 ambushed Li Jiancheng and Li Yuanji, killing them. During the subsequent battles between Li Shimin's forces and Li Jiancheng's and Li Yuanji's forces, Hou led Li Shimin's forces. Following these battles, Li Shimin effectively forced Emperor Gaozu to make him the crown prince, and then to yield the throne to him (as Emperor Taizong).
During Emperor Taizong's reign
Late In 626, when Emperor Taizong personally ranked the contributions of the generals and officials in order to grant them fiefs, Emperor Taizong ranked five of them—Hou Junji, Zhangsun Wuji, Fang Xuanling, Du Ruhui, and Yuchi Gong to be contributors of the highest grade, and Hou was created the Duke of Lu.
In 630, Emperor Taizong made Hou the minister of defense and gave him the additional designation of Canyi Chaozheng (), making him a de facto chancellor.
In 634, Emperor Taizong, sending the senior general Li Jing to command the campaign against Tuyuhun's Busabo Khan Murong Fuyun, made Hou and Li Daozong the Prince of Rencheng Li Jing's assistants on the campaign. By spring 635, Tang forces achieved initial victories, but Tuyuhun forces then burned the grazing grass to cut the food supplies to Tang horses. Most Tang generals wanted to withdraw, but Hou advocated continued advance, and Li Jing agreed, eventually allowing complete victory, as Murong Fuyun was killed by his subordinates, allowing his son Murong Shun, whom Tang supported, to become khan (as Yidou Khan). Around the new year 636, after Murong Shun was assassinated by his subordinates, Emperor Taizong sent Hou with an army to try to secure the throne for Murong Shun's son Murong Nuohebo.
In 637, as part of Emperor Taizong's scheme to bestow prefectures on his relatives and great generals and officials as their permanent domains, Hou's title was changed to Duke of Chen, and he was given the post of prefect of Chen Prefecture (陳州, roughly modern Zhoukou, Henan), to be inherited by his heirs. Soon, however, with many objections to the system, the strongest of which came from Zhangsun Wuji, Emperor Taizong cancelled the scheme, although Hou's title remained Duke of Chen.
In 638, Tufan's Songtsen Gampo, after hearing that the rulers of Tujue and Tuyuhun were all able to marry Tang princesses, requested to marry one as well, but was rebuffed by Emperor Taizong. In anger, he launched a major attack on Tang, capturing a number of prefectures. Emperor Taizong sent Hou to counterattack, assisted by other generals Zhishi Sili (), Niu Jinda (), and Liu Jian (). Niu was subsequently able to defeat Tufan forces at Song Prefecture (松州, roughly modern Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan), and Songtsen Gampo, in fear, withdrew, but still requested to marry a Tang princess. (This time, Emperor Taizong agreed, sending Princess Wencheng, a daughter of a clansman, to marry Songtsen Gampo.)