Zhang Xianzhong (張獻忠 or Chang Hsien-chung; 18 September 1606 – 2 January 1647), courtesy name Bingwu (秉吾), art name Jingxuan (敬軒), was a Chinese peasant leader who led a peasant rebellion from Yan'an wei, Shaanxi (today Yulin, Shaanxi province) during the Ming-Qing transition. He conquered Sichuan in 1644, and named himself king and later emperor of the Xi dynasty. His rule in Sichuan was brief, and he was killed by the invading Qing army. He is commonly associated with the massacres in Sichuan that depopulated the region. However, the extent of his killings is disputed.

Zhang was born in Liushujian (柳树涧; literally 'willow spring', modern Dingbian, Shaanxi province), in 1606 into a poor family. He was described as tall in stature, had a yellow complexion and a "tiger chin" (虎頷, meaning an impressive beard), and hence was given the nickname "Yellow Tiger". In the mid-1620s, he enlisted in the Ming army. He was sentenced to death for breaching military law. He was reprieved after a senior officer intervened, impressed by Zhang's demeanour.

Towards the end the Ming dynasty, drought, famines and epidemics broke out in various parts of China. In the late 1620s, peasants revolted in Shaanxi, resisting attempts by the Ming government to collect grains and taxes. They coalesced into rebel armies called "roving bandits" (liúkòu 流寇) because of their highly mobile nature, and spread into other parts of China. Zhang deserted from the army around 1630, joined the rebel forces in Mizhi County, and established himself as a rebel leader with a few hundred followers, styling himself Bada Wang (八大王, Eighth Great King). Among his followers was his adopted son Li Dingguo. His mobile forces would conduct raids along the western edge of Shaanxi, plundering swiftly and hiding out in the hills. Later he moved into other provinces, moving from place to place raiding towns and cities. He made forays into Sichuan by the late 1633 but was repelled by Qin Liangyu. He was also defeated at various times by the Ming forces; Zhang would also surrender when it was expedient for him to do so, for example in 1631 and 1638, but would then later regroup and resume the rebellion.

In 1635, Zhang joined a larger confederation of bandits with other rebel leaders including Li Zicheng (Li would later capture Beijing and end Ming rule there). They devastated Henan and pushed into Anhui. After they had burnt the Ming ancestral temple at Zhongdu (Fengyang) in Anhui and ravaged the area, the rebel armies broke up and Zhang headed to Huguang (now Hubei). He failed to subdue the city of Luzhou, but captured Xiangyang with 70,000 men under his command the following year in 1636. In 1637, joined by other rebels and with an army now reaching a size of 300,000 men, he again pushed into Anhui, then to Jiangsu to capture Suzhou, and almost down to Nanjing, auxiliary capital of Ming. But he was immediately defeated there and he retreated back to Huguang. He besieged Chengdu in 1637 but failed to take it. In 1638, Zhang was injured in a battle in Huguang with Ming general Zuo Liangyu, and he then surrendered to Ming supreme commander Xiong Wencan (熊文燦) who believed in peaceful suasion, and was allowed to settle in Gucheng and serve as a regional Ming commander. However, he reneged on the agreement in early 1639 and rebelled, killing the local prefect and burning the town. He then ambushed and inflicted heavy losses to the Ming forces led by the Ming general Zuo Liangyu. In 1640, he suffered a defeat at the hand of Zuo at Mount Manao in Sichuan, and was forced to flee with his few remaining followers to hide in the mountains of Eastern Sichuan for a few months.

Zhang gathered the remnants of his forces, and continued with his raids which Ming commander Yang Sichang found hard to contain. In 1641, he emerged from Sichuan and attacked Xiangyang, capturing and executing the imperial Prince of Xiang there. Zhang's army swelled as he took a number of towns and cities such as Sucheng, Luzhou and Tongcheng, and declined when he suffered setbacks at the hands of Ming generals Zuo Liangyu. In 1643, he took Macheng in Huguang, and his army swelled to some 57,000 after incorporating the city's rebels. He then captured the provincial capital of Wuchang, killed the imperial prince there, and proclaimed himself "Xi Wang" (King of the West). He attempted to set up a government in Wuchang, but abandoned the city after two months when Ming forces gathered strength, and captured Wuchang soon after Zhang left. With an army of 200,000, Zhang took Yuezhou, Hengzhou and Changsha, and for a while Zhang stayed at Changsha where he controlled much of Hunan and part of Jiangxi.

In 1644, Zhang decided to abandon Hunan and led 100,000 of his troops towards Sichuan. His army converged on Chongqing from two directions and surrounded the city. After several days of fighting, his army managed to blast a hole through the city wall and captured the city on 25 July 1644. He was said to have cut off the hands of the city's defenders and massacred a large number of people.

The conquest of some other parts of Sichuan was made easier after he promised not to harm the local population if they seized their officials, took possession of the storehouse and surrendered without resistance. He took Chengdu on 9 September 1644, and met no real opposition in the rest of Sichuan afterwards. He then set up court in Chengdu, which he renamed Xijing (西京, Western Capital), and declared himself king of the Xi dynasty (大西王朝, Great Western dynasty). In the 10th lunar month of 1644 he declared himself as emperor with the reign title Dashun.

In Sichuan, Zhang tried to set up a civil administration. Initially, he won much support. According to an account by Gabriel de Magalhães, a Portuguese Jesuit who was working in Sichuan with another Jesuit Lodovico Buglio (but both pressed to serve as astronomers to Zhang), "he began his rule with such liberality, justice and magnificence by which he captivated all hearts that many mandarins, famous both in civic as in military affairs whom fear was keeping concealed, left their hideouts and flew to his side."