Emperor Hui of Jin (simplified Chinese: 晋惠帝; traditional Chinese: 晉惠帝; pinyin: Jìn Huì Dì; Wade–Giles: Chin Hui-ti; 259 – January 8, 307[2]), personal name Sima Zhong (司馬衷), courtesy name Zhengdu (正度), was the second emperor of the Western Jin dynasty.

Emperor Hui was a developmentally disabled ruler, and throughout his reign, there was constant internecine fighting between regents, imperial princes (his uncles, half-brothers and cousins), and his wife Empress Jia Nanfeng for the right to control him (and therefore the imperial administration), causing great suffering for the people and greatly undermining the stability of the Western Jin dynasty, eventually leading to rebellions of the Five Barbarians that led to Jin's loss of northern and central China and the establishment of the competing Sixteen Kingdoms.

As Crown Prince Zhong grew in age, his developmental disabilities became clear to his parents and the imperial officials alike.

They had four daughters during their marriage, but she would not bear his only son Sima Yu—whose mother Consort Xie Jiu was originally a concubine of Emperor Wu, but had been given to Crown Prince Zhong prior to his marriage to Crown Princess Jia, so that Consort Xie could teach him how to have sexual relations.

During his 16-year reign, Emperor Hui would come under the control of a number of regents and de facto princes, never being able to assert authority on his own.

The rough succession order of the regents and de facto princes were: Yang Jun quickly showed himself to be autocratic and incompetent, drawing the ire of many other nobles and officials.

He knew Emperor Hui's empress Jia Nanfeng to be strong-willed, alert to court intrigues, fearless in power plays, ambitious and treacherous, so he tried to put people loyal to him in charge of all the defense forces of the capital Luoyang, and also ordered that all edicts not only be signed by the emperor but also by Empress Dowager Yang before they could be promulgated.

In April 291, after Sima Wei returned to Luoyang from his defense post (Jing Province (荊州, modern Hubei and Hunan)) with his troops, a coup went into progress.

Empress Jia, who had her husband easily under her control, had him issue an edict declaring that Yang Jun had committed crimes and should be removed from his posts.

To appease those who might have been angry and had overthrown Yang Jun, Sima Liang also widely promoted those who participated in the plot, and more than a thousand men were created marquesses.

Empress Jia, who had already resented Wei for having suggested that the heir selection be changed during Emperor Wu's reign, desired more direct control over the government, and therefore resolved to initiate a second coup d'état.

His forces thereby surrounded Sima Liang and Wei's mansions, and while both men's subordinates recommended resistance, they each declined and were easily captured.

Contrary to the edict's terms, both were killed—Sima Liang with his heir Sima Ju (司馬矩) and Wei with nine of his sons and grandsons.

She lacked self-control, and was violent and capricious in her ways, but Zhang, Pei, and Jia Mo were honest men who generally kept the government in order.

However, as she grew increasingly unbridled in her behavior (including committing adultery with many men and later murdering them to silence them), Zhang, Pei, and Jia Mo considered deposing her and replacing her with Crown Prince Yu's mother Consort Xie, but they hesitated and never took actual action.

In 297, the Jin general Zhou Chu (周處), without support from the central government, was easily defeated by Qi.

A large group of refugees, most of Di ancestry, stricken by the famine that resulted from the warfare, fled south into Yi Province (modern Sichuan and Chongqing), led by Li Te.

When Crown Prince Yu was in the palace to make an official petition to have his ill son Sima Bin (司馬彬) created a prince, Empress Jia forced him to drink a large amount of wine and, once he was drunk, had him write out a statement in which he declared intention to murder the emperor and the empress and to take over as emperor.

Empress Jia presented the writing to the officials and initially wanted Crown Prince Yu executed—but after some resistance, she only had him deposed and reduced to the status of a commoner in February.

He had his sons created princes, and ran the matters of the central government from his mansion, rarely visiting the emperor or attending the imperial meetings.

Sima Ai, of the princes, appeared to be the only one who saw the importance of formally honoring Emperor Hui while maintaining resemblance to impartial governance.

At the same time of Li's successes, many agrarian rebellions also started throughout the empire, including one that defeated the forces of the powerful Sima Xin the Prince of Xinye and killed him.

Wang Jun, the military commander of You Province (幽州, modern Beijing, Tianjin, and northern Hebei), who had an uneasy relationship with Sima Ying up to this point, then declared war against Sima Ying and headed south with his troops, allied with various Xianbei and Wuhuan tribes.

Sima Ying found it difficult to resist them, and he sent one of his subordinates, the Xiongnu noble Liu Yuan, to his own tribesmen to ask them to join him.

(A month earlier, Li Xiong had declared himself independent of Jin as well, as the Prince of Chengdu, establishing Cheng Han; these two states would be the first two of the Sixteen Kingdoms.)

Sima Yong also had Zhang Fang forcibly move Emperor Hui to Chang'an (in modern Xi'an, Shaanxi), directly under his own grasp.

Meanwhile, Han-Zhao attracted those Han and non-Han agrarians and tribesmen disappointed in Jin rule, and began to grow in size and power.

With Sima Yue effectively controlling the government, Emperor Hui reigned for several months until 8 January 307, when, for unknown reasons, he was poisoned while eating bread.

Crown Prince Chi succeeded him (as Emperor Huai) and would try to restrengthen the empire, but it was too late for Jin by that point.

Emperor Hui fainted, and when he woke up in Ye, he forbid his servants from washing the clothes, exclaiming, "This is the blood of Attendant Ji (Shao).