Cui Dunli was born in 596, originally named Cui Yuanli, His family was from "the second house of Boling" of the prominent Cui clan of Boling, although by the end of Northern Wei it had already relocated to Yong Prefecture. Cui Dunli's grandfather Cui Zhongfang served as the minister of ceremonies during Sui Dynasty. It was said that Cui studied biographies and had sought to keep himself faithful and righteous.
During Emperor Gaozu's reign
During the reign of Tang's founder Emperor Gaozu, Cui Dunli served as a mid-low-level official at the legislative bureau of government. It was said that he was skillful with his words and always acted appropriately, so much so that people were intimidated when they saw him. It was during Emperor Gaozu's reign that Emperor Gaozu changed his name from the original Yuanli to Dunli, although the reason was not stated in historical records. In 626, Emperor Gaozu's son Li Shimin the Prince of Qin, locked in an intense sibling rivalry with his older brother and Emperor Gaozu's oldest son, Li Jianchengthe Crown Prince, killed Li Jiancheng and another brother who supported Li Jiancheng, Li Yuanji the Prince of Qi at the Incident at Xuanwu Gate and effectively seized power. Emperor Gaozu's distant nephew Li Yuan the Prince of Lujiang, who was then commandant at You Prefecture, was an ally of Li Jiancheng's, and when Li Shimin sent Cui to You Prefecture to summon Li Yuan to the capital Chang'an. Li Yuan became fearful, and at the instigation of his deputy Wang Junkuo started a rebellion. He seized Cui and tried to force Cui to reveal military secrets of the imperial army, but Cui refused. Soon, Wang himself rebelled against Li Yuan and seized him, surrendering to the imperial forces. Upon Cui's return to Chang'an, Li Shimin made him a commander of the imperial guards and awarded him with gold and good horse.
During Emperor Taizong's reign
Later in 626, Emperor Gaozu passed the throne to Li Shimin, who took the throne as Emperor Taizong. In 627, Emperor Taizong promoted Cui Dunli to a higher post within the legislative bureau. It was said that particularly because Cui admired the great Han Dynasty diplomat Su Wu, he was frequently sent as a diplomat to Eastern Tujue. At a later point, Cui became the deputy minister of defense, a post that he still held as of 642, when he was sent to Eastern Tujue's successor stateXueyantuo to negotiate a marriage of Emperor Taizong's daughter Princess Xinxing with Xueyantuo's Zhenzhu Khan Yi'nan, in order to gain the release of the general Qibi Heli, who had been held captive by Xueyantuo. He later served as the commandant at Ling Prefecture, and then was summoned back to Chang'an to serve as minister of defense. He was serving in that post as of 646, when he was sent to negotiate the surrender of Yi'nan's nephew the Yitewushi Khan Duomozhi, although apparently before he could arrive, Duomozhi surrendered to the general Li Shiji. After Xueyantuo's collapse, its vassal Huige briefly took over its territory, but Huige itself was severely weakened in 648 when its ruler Yaoluoge Tumidu was assassinated by his nephew Yaoluoge Wuge. Emperor Taizong, apprehensive that Huige would collapse and lead to a new round of disturbances, sent Cui to pacify the Huige people and to create Yaoluoge Tumidu's son Yaoluoge Porun as the new ruler of Huige.
During Emperor Gaozong's reign
In 649, Emperor Taizong died and was succeeded by his son Li Zhi. Cui Dunli continued to serve as minister of defense, and in 652, he commissioned Cui with an army to gather the remaining tribesmen of Xueyantuo to force them relocate to Qilian Prefecture. Later that year, Emperor Gaozong's sister Princess Gaoyang, her husband Fang Yi'ai, Emperor Gaozong's uncle Li Yuanjing the Prince of Jing, Emperor Gaozong's brother Li Ke the Prince of Wu, another brother-in-law Chai Lingwu, and the general Xue Wanche, were implicated in a plot to overthrow Emperor Gaozong and replace him with Li Yuanjing. Some of them were executed, and some were ordered to commit suicide. Emperor Gaozong initially wanted to spare Li Yuanjing and Li Ke, but at Cui's opposition did not do so. In 653, Cui was made Shizhong -- the head of the examination bureau of government and a post considered one for a chancellor. He became in charge of editing imperial histories, and he was created the Duke of Gu'an. In 655, he was made Zhongshu Ling, the head of the legislative bureau and still a chancellor post. In 656, Cui, who had been given an additional post as a staff member of Emperor Gaozong's son and crown prince Li Hong as well, offered to resign on account of illness. Emperor Gaozong gave him the post as an advisor to Li Hong and no longer let him serve as Zhongshu Ling, but gave him the designation of Tong Zhongshu Menxia Sanpin, making him a chancellor de facto. Emperor Gaozong also recalled Cui's younger brother Cui Yuqing, who was then serving as the military advisor to the commandant at Dingxiang, from Dingxiang, to attend to Cui Dunli. Cui Dunli died less a month later. Emperor Gaozong personally led a public mourning and buried him with honors, near Emperor Taizong's tomb.
