Liu Yan (traditional Chinese: 劉龑; simplified Chinese: 刘䶮; pinyin: Liú Yǎn; Jyutping: Lau4 Jim2; 889 – 10 June 942), né Liu Yan (劉巖), also named Liu Zhi (劉陟) (from c. 896 to 911) and briefly as Liu Gong (劉龔), also known by his temple name as the Emperor Gaozu of Southern Han (南漢高祖), was the first emperor of the Chinese Southern Han dynasty, one of the Ten Kingdoms during the Five Dynasties and Ten Kingdoms period.

Liu Yan was born in 889, during the reign of Emperor Zhaozong of Tang. His father Liu Zhiqian (also known as Liu Qian) was then the prefect of Feng Prefecture (封州, in modern Fengkai, Guangdong) and was married to a Lady Wei, the niece of Wei Zhou (韋宙), a prior military governor (Jiedushi) of Lingnan East Circuit (嶺南東道, headquartered in modern Guangzhou, Guangdong), which Feng Prefecture belonged to. However, he also secretly had a concubine outside the home, a Lady Duan, and it was to Lady Duan that Liu Yan was born. When Lady Wei found out, she killed Lady Duan, but could not bear to kill the infant Liu Yan, and she took him back home to be raised as her own, as a younger brother to her own sons Liu Yin and Liu Tai (劉臺).

As Liu Yan grew up, it was said that he was tall and capable in both horsemanship and archery. After Liu Yan became the commander of the army of the circuit (which had been renamed Qinghai (清海) by that point under the military governor Li Zhirou the Prince of Xue in 896, Liu Yan was also given the title of military advisor to Li Zhirou as the Prince of Xue, and his name was changed from Liu Yan to Liu Zhi.

In 901, Li Zhirou's successor Xu Yanruo died, leaving a recommendation to Emperor Zhaozong that Liu Yin be made acting military governor, and Liu Yin subsequently took that title. Liu Zhi continued serving under his brother, and was first recorded to have participated in a campaign in 902, when Lu Guangchou, who controlled the Qian Prefecture (虔州, in modern Ganzhou, Jiangxi) region as Qian's prefect, attacked Qinghai, capturing Shao Prefecture (韶州, in modern Shaoguan, Guangdong) and giving it to his son Lu Yanchang, and then putting Chao Prefecture (潮州, in modern Chaozhou, Guangdong) under siege. Liu Yin personally led an army and repelled Lu Guangchou from Chao, and then prepared to attack Shao. Under Liu Zhi's advice (as Liu Zhi believed that a direct attack would not be successful due to the strength of Lu Yanchang's army), he put Shao under siege to try to wear out Lu Yanchang's defense, but the strategy backfired when, due to high water levels on the river, the Qinghai army's food supplies were disrupted. Lu Guangchou then launched a relief army from Qian, repelling Liu Yin from Shao.

Meanwhile, Emperor Zhaozong commissioned the chancellor Cui Yuan as the new military governor of Qinghai, but Cui, while on the way to Qinghai, heard about popular uprisings in the region and also was worried that Liu Yin would not yield the position to him, and therefore returned to then-capital Luoyang. Subsequently, after Liu Yin bribed the powerful warlord Zhu Quanzhong the military governor of Xuanwu Circuit (宣武, headquartered in modern Kaifeng, Henan), who had the Tang imperial court under his physical control by that point, Emperor Zhaozong's son and successor Emperor Ai of Tang commissioned Liu Yin as full military governor in 904. Liu Zhi served as Liu Yin's deputy military governor. It was said that at that time, in addition to the continued conflict with Lu Guangchou, substantial portions of the region were controlled by other warlords—Khúc Hạo (曲顥) at Jiao Prefecture (交州, in modern Hanoi, Vietnam); Liu Shizheng (劉士政) at Gui Prefecture (桂州, in modern Guilin, Guangxi); Ye Guanglüe (葉廣略) at Yong Prefecture (邕州, in modern Nanning, Guangxi); Pang Juzhao (龐巨昭) at Rong Prefecture (容州, in modern Rong County, Guangxi); Liu Changlu (劉昌魯) at Gao Prefecture (高州, in modern Gaozhou, Guangdong); and Liu Qian (劉潛, different person than Liu Zhi's father) at Xin Prefecture (新洲, in modern Yunfu, Guangdong). In addition, east of the Pearl River, there were some 70 camps of people who did not recognize Liu Yin's authorities. It was said that after Liu Yin entrusted the military matters to Liu Zhi, Liu Zhi gradually had these warlords expelled or forced into submission, such that he became known as the preeminent general in the Lingnan region.

One of these campaigns was described as in or around 910 (by which time Liu Yin was a vassal of the new Later Liang, which Zhu had established as its Emperor Taizu, and carried the title of Prince of Nanping or Nanhai), when Liu Zhi attacked Liu Changlu at Gao Prefecture. Liu Changlu repelled his attack, but figured that he would not be able to indefinitely hold out against the Liu brothers, and therefore, along with Pang, offered to submit to Ma Yin the Prince of Chu. Ma sent troops to safely escort Liu Changlu and Pang back to his territory and had his general Yao Yanzhang take up garrison at Rong Prefecture.

In 911, Liu Yin grew deathly ill. He submitted a petition recommending Liu Zhi as acting military governor, and died shortly after. Liu Zhi took over the circuit. Shortly after, Later Liang's Emperor Taizu made Liu Zhi full military governor. His name was changed back to Liu Yan.

It was said that Liu Yan, while serving as military governor, frequently invited members of the intelligentsia who had fled from the Central Plain to serve on his staff, and often made them prefects of the circuit's prefectures, so among the prefects there were no military officers.