Fu Deng (; 343–394) was an emperor of the Di-led Chinese Former Qin dynasty. He assumed the throne in 386 after the deaths of Fu Jiān (Emperor Xuanzhao) and Fu Jiān's son Fu Pi (Emperor Aiping), even though he was only a distant relative of theirs, as by that time Former Qin's territory had largely been reduced to the territory under his control. He battled the Later Qin emperor Yao Chang for years in a stalemate that neither could conclusively prevail, but in 394, he made a major attack on Later Qin after Yao Chang's death, seriously underestimating Yao Chang's son and successor Yao Xing, who captured and executed him. Later that year, his son Fu Chong, who succeeded him, would die in battle, ending Former Qin.
Early career
Fu Deng was born in 343, to Fu Chang (苻敞), a distant grandnephew of Former Qin's founder Fu Jiàn, while still under Later Zhao rule. After Fu Jiàn founded Former Qin in 351, Fu Chang served as a general and a commandery governor. During the reign of Fu Jiàn's cruel and whimsical son Fu Sheng (r. 355–357), Fu Chang was executed, but he was posthumously honored after Fu Sheng was overthrown by his cousin Fu Jiān. Fu Jiān was impressed by Fu Deng's abilities, and when he grew older, Fu Deng was made the county magistrate of the capital Chang'an. Later, however, for unspecified faults, he was demoted to be the county magistrate for Didao (狄道, in modern Dingxi, Gansu).
After Former Qin began to collapse in 384 and Fu Jiān was killed by the Later Qin general Yao Chang in 385, Fu Deng became a subordinate of the general Mao Xing (毛興), who sought to control all of the provinces in the west still nominally under Former Qin rule, but his soldiers became weary from all of the battles and assassinated him in 386, replacing him with Wei Ping (衛平), a very old general who was the head of the clan. However, these soldiers soon became convinced that Wei was too old to accomplish much, and they deposed Wei and replaced him with Fu Deng. Fu Deng submitted a report of these events to Fu Jiān's son Fu Pi, the new emperor, and Fu Pi commissioned him as a provincial governor and created him the Prince of Nan'an.
The battles between Fu Deng and Yao Chang after the former replaced Wei Ping coincided with a time of droughts and famines. Fu Deng called the killed enemies shóushí (熟食, "cooked food" or "readied food") and told his soldiers, "Fight in the morning and you will have meat to eat in the evening. Why worry about hunger?" The soldiers followed his order, ate the corpses, and had the force for battles. Hearing this, Yao Chang hurried to call his brother Yao Shuode (姚碩德) for help, saying, "If you do not come, we are going to be eaten off by Fu Deng."
Later in 386, Fu Pi died in battle against Jin, and the territory under his direct control (modern Shanxi), as well as his officials, fell into the hands of the Western Yan emperor Murong Yong. His official Kou Qian (寇遣) escorted his sons Fu Yi (苻懿) the Prince of Bohai and Fu Chang (苻昶, note different character than Fu Deng's father) the Prince of Jibei to Fu Deng's domain. Fu Deng, after mourning for Fu Pi, proposed to have Fu Yi declared emperor, but his subordinates all opined that given the state Former Qin was in (down to holding not much more than the territory under Fu Deng's control), the state needed an older emperor; at their suggestion, Fu Deng himself took the throne. He made Fu Yi his crown prince.
Reign
Before the Battle of Dajie
Even before he took imperial title, Fu Deng battled Yao Chang continuously, and the wars between Fu Deng and Yao Chang's Later Qin intensified after Fu Deng became Former Qin's emperor. Fu Deng set up a shrine to Fu Jiān in his army, and whenever he made a key decision he would report it to Fu Jiān. He was also described as a master of square and circular formations (although the exact mechanism is not understood well), and initially won a number of battles over Later Qin—so much so that Yao Chang, in fear, also set up a shrine dedicated to Fu Jiān in his army, apologizing for his killing of Fu Jiān and requesting forgiveness. However, after that failed to yield victories, Yao Chang cut off the head of the effigy he had made of Fu Jiān and delivered to Fu Deng. But Fu Deng's victories over Yao Chang did not appear to have lasting impact, and the wars between Former Qin and Later Qin became stalemated. Meanwhile, Fu Deng's shortcomings became exposed—an inability to take decisive action to deal heavy damage to Later Qin, and Yao Chang took advantage of his indecisive tendencies to gradually destroy other semi-independent generals in the Guanzhong region and consolidate his power base.
