Emperor Gaozu of Han in the context of "Law enforcement officer"

The emperors of the Han dynasty were the supreme heads of government during the second imperial dynasty of China; the Han dynasty (202 BC – 220 AD) followed the Qin dynasty (221–206 BC) and preceded the Three Kingdoms (220–265 AD). The era is conventionally periodised into the Western Han (202 BC – 9 AD) and Eastern Han (25–220 AD).

The Han dynasty was founded by the peasant rebel leader Liu Bang, known posthumously as Emperor Gao (r. 202–195 BC). The longest reigning emperor of the dynasty was Emperor Wu (r. 141–87 BC), who reigned for 54 years. The dynasty was briefly interrupted by the Xin dynasty of the former regent Wang Mang, but he was killed during a rebellion on 6 October 23 AD. The Han dynasty was reestablished by Liu Xiu, known posthumously as Emperor Guangwu (r. 25–57 AD) or Guangwu Di, who claimed the throne on 5 August 25 AD. The last Han emperor, Emperor Xian (r. 189–220 AD), was a puppet monarch of Chancellor Cao Cao (155–220 AD), who dominated the court and was made King of Wei. On 11 December 220, Cao's son Pi usurped the throne as Emperor Wen of Wei (r. 220–226 AD) and ended the Han dynasty.

The Han dynasty (202 BCE – 220 CE) was a period of Imperial China divided into the Western Han (202 BCE – 9 CE) and Eastern Han (25–220 CE) periods, when the capital cities were located at Chang'an and Luoyang, respectively. It was founded by Emperor Gaozu of Han and briefly interrupted by the regime of Wang Mang (r. 9–23 CE) who usurped the throne from a child Han emperor.

The Han dynasty was an age of great economic, technological, cultural, and social progress in China. Its society was governed by an emperor who shared power with an official bureaucracy and semi-feudal nobility. Its laws, customs, literature, and education were largely guided by the philosophy and ethical system of Confucianism, yet the influence of Legalism and Daoism (from the previous Zhou dynasty) could still be seen. Members of the scholarly-gentry class who aspired to hold public office were required to receive a Confucian-based education. A new synthetic ideology of Han Confucianism was created when the scholar Dong Zhongshu (179–104 BCE) united the Confucian canon allegedly edited by Kongzi, or Confucius (551–479 BCE), with cosmological cycles of yin and yang and the Chinese five elements.

Han (漢; 221–263), known in historiography as Shu Han (蜀漢 [ʂù xân] ) or Ji Han (季漢 "Junior Han"), or often shortened to Shu (Chinese: 蜀; pinyin: Shǔ; Sichuanese Pinyin: Su < Middle Chinese: *źjowk < Eastern Han Chinese: *dźok), was a dynastic state of China and one of the three major states that competed for supremacy over China in the Three Kingdoms period. The state was based in the area around present-day Hanzhong, Sichuan, Chongqing, Yunnan, Guizhou, and north Guangxi, an area historically referred to as "Shu" based on the name of the past ancient kingdom of Shu, which also occupied this approximate geographical area. Its core territory also coincided with Liu Bang's Kingdom of Han, the precursor of the Han dynasty.

Shu Han's founder, Liu Bei (Emperor Zhaolie), had named his dynasty "Han", as he considered it a rump state of the Han dynasty and thus the legitimate successor to the Han throne, while the prefix "Shu" was first used by the rival state of Cao Wei to delegitimize the claims of the Shu Han state to orthodox succession. Later on when writing the Records of the Three Kingdoms, the historian, Chen Shou, also used the prefix "Shu" to describe Liu Bei's state of Han as a historiographical prefix to differentiate it from the many other states officially named "Han" throughout Chinese history.

Han Xin (simplified Chinese: 韩信; traditional Chinese: 韓信; pinyin: Hán Xìn; Wade–Giles: HanHsin; died c.March 196 BCE) was a Chinese military general and politician who served Liu Bang during the Chu–Han Contention and contributed greatly to the founding of the Han dynasty. Han Xin was named as one of the "Three Heroes of the early Han dynasty" (Chinese: 漢初三傑), along with Zhang Liang and Xiao He.

Han Xin is best remembered as one of the most brilliant military commanders in Chinese history, renowned for his exceptional strategic intellect and tactical mastery. His innovative use of deception, maneuver warfare, and battlefield psychology set new standards in military art, with several of his campaigns serving as textbook examples of effective command. Han Xin's application of warfare principles not only exemplified but at times expanded upon the teachings of The Art of War, with some of his tactics giving rise to enduring Chinese idioms. Undefeated in every engagement he commanded, his victories were instrumental in the founding of the Han dynasty. For his extraordinary accomplishments, Han Xin earned the legendary title of "God of War" (兵仙) in later Chinese tradition.

Heqin, also known as marriage alliance, refers to the historical practice of Chinese monarchs marrying princesses—usually members of minor branches of the ruling family—to rulers of neighboring states. It was often adopted as an appeasement strategy with an enemy state that was too powerful to defeat on the battlefield. The policy was not always effective. It implied an equal diplomatic status between the two monarchs. As a result, it was controversial and had many critics.

Lou Jing, the author of the policy, proposed granting the eldest daughter of Emperor Gaozu of Han to Modu Chanyu of the Xiongnu. His proposal was adopted and implemented with a treaty in 198 BC, following the Battle of Baideng two years prior. Wang Zhaojun, of the Han dynasty, and Princess Wencheng, of the Tang dynasty, are among the most famous heqin princesses.

Xiang Liang (項梁; died 208 BC) was a Chinese military leader who led a rebellion against the Qin dynasty between 209 and 208 BC. He is best known as an uncle of Xiang Yu, the rival of the Han dynasty's founding emperor Liu Bang during the Chu–Han Contention.

Zhang Han (died c. June or July 205 BC) was a Chinese military general of the Qin dynasty. Between 209 and 208 BC, when uprisings against the Qin dynasty broke out, Zhang Han, along with Sima Xin and Dong Yi, led Qin forces into battle against the various rebel groups and defeated some of them. However, they lost to rebel forces led by Xiang Yu in 207 BC at the Battle of Julu and were forced to surrender. After the rebels overthrew the Qin dynasty in 206 BC, China was divided into the Eighteen Kingdoms and the three surrendered Qin generals were made kings – Zhang Han as the King of Yong, Sima Xin as the King of Sai, and Dong Yi as the King of Di. Their three kingdoms were collectively known as the Three Qins since they occupied the Guanzhong region, the heartland of the Qin state during the Warring States period. In 205 BC, Liu Bang, the King of Han, invaded Zhang Han's kingdom and defeated Zhang Han in battle. Zhang Han committed suicide after his defeat.

Fan Zeng (范增; 277–204 BC) was an adviser to the Chinese warlord Xiang Yu, who fought for supremacy over China during the Chu–Han Contention (206–202 BC) with Liu Bang, the founding emperor of the Han dynasty.

Emperor Wen of Han (Chinese: 漢文帝; 203/02 – 6 July 157 BC), personal name Liu Heng (劉恆), was the fifth emperor of the Han dynasty from 180 until his death in 157 BC. The son of Emperor Gao and Consort Bo, his reign provided a much needed stability within the ruling Liu clan after the unstable and violent regency of Empress Lü, who went after numerous members of the clan. The prosperous reigns of Emperor Wen and his son Emperor Jing are highly regarded by historians, being referred to as the Rule of Wen and Jing. He was one only four Western Han emperors to receive a temple name, along with Emperor Gaozu, Emperor Wu, and Emperor Xuan of Han.

When Emperor Gaozu suppressed the rebellion of Dai (代), he made Liu Heng Prince of Dai. Since Emperor Gaozu's death, power had been in the hands of his wife, Empress Lü, the empress dowager. After Empress Lü's death, the officials eliminated the powerful Lü clan, and deliberately chose the Prince of Dai as the emperor, since his mother, Consort Bo, had no powerful relatives, and her family was known for its humility and thoughtfulness.