Wang Jun (252 – 4 April 314), courtesy name Pengzu, was a military general and warlord of the Western Jin dynasty of China. By the time of Sima Lun's usurpation of the Western Jin throne, he was established as a military commander in You Province. Although he became a target of Sima Ying as the War of the Eight Princes unfolded, he survived the chaos, ultimately supporting Sima Yue's faction. At the time of the Disaster of Yongjia which saw the collapse of Jin control in northern China, he was one of Jin's few remaining provincial powers in the north. However among claims of imperial ambitions and corruption, he clashed not only with northern tribal powers but also his Jin dynasty rival Liu Kun the Inspector of Bingzhou, before his final defeat and death at the hands of Shi Le, who had previously won Wang Jun's trust.

Wang Jun was born to a concubine of Wang Chen of the prominent Wang clan of Jinyang County (晉陽; southwest of present-day Taiyuan, Shanxi) in Taiyuan commandery. His mother was from a poor commoner family, so Wang Chen refused to acknowledge Wang Jun as his son. Only Wang Jun's uncle, Wang Hun, saw potential in him and believed he would one day be a part of the Three Excellencies in times of chaos. In 266, Wang Chen died without a legitimate son, so his relatives established Wang Jun, then aged 14, as his heir. Wang Jun inherited Wang Chen's title of Duke of Boling and was appointed Chief Commandant of Escorting Cavalry by the court.

Wang Jun became a Regular Mounted Attendant in 282. In 291, the court transferred him to serve as a Regular Attendant and later moved him to Commandant of the Surpassing Riders and General of the Right. Soon, Wang Jun became the Imperial Corps Commander and guarded Xuchang.

In 299, during Empress Jia's rule behind the curtains, she had the Crown Prince, Sima Yu, under house arrest in Xuchang. The following year, Wang Jun and the eunuch Sun Lü (孫慮) assisted her in poisoning Sima Yu. Wang Jun received the title General Who Pacifies The North and Imperial Inspector of Qingzhou. After a while, the court moved him to General Who Calms The Northern Frontiers and Chief Controller of Youzhou. While in Youzhou, Wang Jun sensed that civil war would soon ensue in northern China. Thus, he began initiating alliances with the neighbouring barbarian tribes to secure his position. He married his two daughters; one to the chieftain of the Xianbei Duan tribe, Duan Wuwuchen and another to a general of the Xianbei Yuwen tribe, Sunuyan (素怒延).

In 301, Emperor Hui of Jin's regent, Sima Lun, deposed Hui and declared himself emperor. The three princes, Sima Ying, Sima Yong and Sima Jiong, promptly began an alliance to restore Emperor Hui. Wang Jun remained neutral throughout the war and refused the send out his troops. He even confiscated letters from the coalition calling to arms in Youzhou to prevent anyone from joining them. Sima Ying was particularly frustrated at Wang Jun's actions and considered attacking him but decided not to due to more pressing issues. After overthrowing Sima Lun, Wang Jun received the office of General Who Secures the North.

In 304, Sima Ying and Sima Yong became Jin's paramount leaders after killing the Prince of Changsha, Sima Ai. While in power, Sima Ying sought to eliminate Wang Jun, still begrudging him for his conduct in 301. Wang Jun himself was also not pleased with the outcome of Sima Ying and Sima Ai's war. Sima Ying appointed his trusted subordinate, He Yan (和演), as Inspector of Youzhou with orders to assassinate Wang Jun. He Yan colluded with the Wuhuan Chanyu, Shen Deng (審登), and when the two travelled with Wang Jun to Qingquan (清泉; south of present-day Beijing), they agreed to have him killed there. However, a heavy storm drenched their troops' equipment and foiled their plans on the day of their attempt.

Shen Deng perceived the storm as a sign that the Heavens favoured Wang Jun, so he defected to Wang Jun and revealed the plot. In response, Wang Jun and Shen Deng besieged He Yan and forced him to surrender. After executing He Yan, Wang Jun assumed total control over Youzhou. Sima Ying tried summoning Wang Jun to court, but Wang Jun camped at Jizhou instead. Wang Jun brought along Duan Wuwuchen and a Wuhuan chieftain, Jiezhu (羯朱), and allied with the Inspector of Bingzhou, Sima Teng. They defeated Sima Ying's general, Wang Bin (王斌), and as they approached Sima Ying's base in Yecheng, Wang Jun's vanguard general, Qi Hong, also defeated Shi Chao. Sima Ying panicked and fled to Luoyang, allowing Wang Jun to occupy his city. The Xianbei had Yecheng sacked and abducted many women from the city. After Wang Jun returned to Jicheng, he executed many of the Xianbei soldiers who partook in the abductions, and around 8,000 bodies reportedly filled the Yi River (易水; in present-day Yi County, Hebei).

In 305, Wang Jun was one of the many governors east of Luoyang to acclaim the Prince of Donghai, Sima Yue, as coalition leader to overthrow Sima Yong and bring Emperor Hui back to Luoyang from Chang'an. Wang Jun lent his Xianbei troops to the Prince of Fanyang, Sima Xiao (司馬虓), which proved vital to defeating Sima Yong's powerful ally, Liu Qiao. Wang Jun later had Qi Hong lead his elite Xianbei and Wuhuan charging cavalry to serve in Sima Yue's vanguard. In June 306, Qi Hong and others entered Chang'an, and Wang Jun's Xianbei troops sacked the city, leaving 20,000 dead in their wake.