Khun Sa (Burmese: ခွန်ဆာ, pronounced [kʰʊ̀ɰ̃ sʰà]; 17 February 1934 – 26 October 2007) was an ethnic Han drug lord and warlord. He was born in Hpa Hpeung village, in the Loi Maw ward of Mongyai, Northern Shan State, Burma. Before he assumed the Shan name "Khun Sa" in 1976, he was known primarily by his Chinese name, Zhang Qifu (simplified Chinese: 张奇夫; traditional Chinese: 張奇夫; pinyin: Zhāng Qífū).

In his early life, Khun Sa received military equipment and training from both the Kuomintang and Burmese Army before claiming to fight for the independence of Shan State and going on to establish his own independent territory. He was dubbed the "Opium King" in Myanmar due to his massive opium smuggling operations in the Golden Triangle, where he was the dominant opium warlord from approximately 1976 to 1996. Although the American ambassador to Thailand called him "the worst enemy the world has", he successfully co-opted the support of both the Thai and Burmese governments at various times. After the American Drug Enforcement Administration uncovered and broke the link between Khun Sa and his foreign brokers, he "surrendered" to the Burmese government in 1996, disbanding his army and moving to Yangon with his wealth and mistresses. After his retirement some of his forces refused to surrender and continued fighting the government, but he engaged in "legitimate" business projects, especially mining and construction. He died in 2007 at the age of 73. Today, his children are prominent businesspeople in Myanmar.

He was primarily known by his Han Chinese name, Chang Chi-fu (Zhang Qifu). When he was three years old, his father died. His mother married a local tax collector, but two years later she died as well. He was raised largely by his Han grandfather, who was the headman of the village in which he was born, Loi Maw. The Han side of his family had been living in Shan State since the 18th century.

He received no formal education but had military training as a soldier with Chinese Nationalist forces that had fled into Burma after the victory of Mao's Communists in 1949.

Although his stepbrothers were sent to missionary schools, the only formal education that Khun Sa received as a boy was spending a few years as a Buddhist novice, and for the rest of his life he remained functionally illiterate. In the early 1950s he received some basic military training from the Kuomintang, which had fled into the border regions of Burma from Yunnan upon its defeat in the Chinese Civil War in 1949. He formed his first independent band of young men when he was sixteen, and when his organization grew to several hundred men he became independent of the Kuomintang. After establishing his independence he frequently switched sides between the government and various rebel armies, as the situation suited him.

In 1963 he re-formed his army into a local "Ka Kwe Ye" ("Home guard") unit, under the control of the northeast command of the Burmese army, which was based in nearby Lashio. In return for fighting local Shan rebels, the government allowed him to use their land and roads to grow and trade opium and heroin. By allowing them to be financed by opium production, the Burmese government hoped that these local militia units could be self-supporting. Many government-supported warlords, including Khun Sa, used their profits from the opium trade to buy large supplies of military equipment from the black markets in Laos and Thailand, and were soon better equipped than the Burmese army.

By the late 1960s Khun Sa was one of the most important and powerful militia leaders in Shan state. He held an important pass in Loi Maw, restricting the movements of local communist rebels. During the period, while he was nominally supporting the Burmese government, he maintained contact with Kuomintang intelligence agents.

Through the 1960s Khun Sa became one of Burma's most notorious drug traffickers. He challenged the local dominance of the Kuomintang remnants in Shan State, but in 1967 he was decisively defeated in a battle involving both the Kuomintang and the Laotian army on the Thai–Burma–Laos border. In that battle he led a convoy of 500 men and 300 mules into Laos, but the convoy was ambushed by Kuomintang forces en route. As the battle was going on, the Laotian army (which was also involved in the opium/heroin trade) bombed the battleground and stole the opium. This defeat demoralized him and his forces. The Laotian army continued to ambush his mule trains for the next few years, and his military strength declined.