Han Gaozu , personal name Liu Bang ( 刘邦 ) , was the first emperor of the Chinese Han Dynasty , ruling over China from 202 BC until 195 BC , and one of only two dynasty founders who emerged from the peasant class. Before becoming an emperor, he was also called Lord Pei ( 沛公 ) after his birthplace.

Liu Bang was born into a peasant family in Pei ( 沛 ) . When he was young, he did not like farm work, and was evidently living a rogue's life. Not surprisingly, he was not the favorite son of his peasant father.

After he was grown up, Liu Bang served as a patrol officer in his county. Once he was responsible of transporting a group of prisoners to Mount Li in now Shanxi province. During the trip many prisoners fled, and when it was obvious that at this rate no one would make to the destination, Liu Bang released all the rest prisoners and fled himself.

In 209 BC Chen Sheng ( 陈胜 ) led an uprising against Qin Dynasty . Pei was in old Chu territory and when many other part of old Chu rebelled, Liu Bang killed the magistrate of Pei County and rebelled himself.

Liu Bang served first as a subordinate of Xiang Liang ( 项梁 ) and then, after Xiang Liang was killed in action, became a subordinate of Xin, King Huai of Chu ( 楚怀王 ) , the nominal leader of all the rebellion kings. King Huai of Chu created Liu Bang as Marquess of Wu'an.

King Huai of Chu made a promise that whoever occupied Guanzhong first should be awarded Guanzhong as his kingdom. He then sent Liu Bang for this mission, partly because he considered Liu Bang a kind and merciful man, partly because he did not like Xiang Yu ( 项羽 ) . When Xiang Yu was busy fighting the main force of Qin Dynasty , Liu Bang invaded Guangzhong with relative ease.

In December 207 BC , the last Qin ruler surrendered to Liu Bang and his rebel army, and in 206 BC Liu Bang entered the Qin capital Xianyang ( 咸阳 ) . However, now Xiang Yu was the most powerful rebel at that time Now considering the whole China was in his hands, Xiang Yu realligned the territories of the rebel kings and created the 18 Kingdoms . Xiang Yu did not honor the promise by King Huai of Chu , who would soon himself be assassinated by Xiang Yu . Instead, he gave Guanzhong to the kings of three Qin . Liu Bang was only awarded the kingdom of Han (Southern part of now Shranxi province).

In Hanzhong, Liu Bang focused his efforts on developing agriculture methods and training an army, through which he reinforced his resource accumulation and military power. Before long, Liu Bang left Hanzhong, deposed the kings of three Qin and occupied Guanzhong, where he launched a war now known as the Chu-Han War , against Xiang Yu .

Although Xiang Yu was far superior in military to Liu Bang, he was short of political maneuover. Xiang Yu kept defeating Liu Bang in the battlefield, but each of his victories only made more people stand by the side of Liu Bang. When Xiang Yu finally was defeated, he could never recovered and commited suicide.

The war lasted four years (206–202 BC) and ended with Liu Bang's victory. Having defeated Xiang Yu, Liu Bang claimed himself emperor and established the Han Dynasty in 202 BC and made Chang'an (present city of Xi'an ) his capital city. Liu Bang became historically known as Emperor Gao of Han.

After Liu Bang came into power, he re-centralised China based on Qin's model. He gradually replaced the original vassals, granting their lands to his relatives. Since the economy had been devastated by the war following the demise of the Qin Dynasty, he reduced taxes and Xiongnu . Under Gaozu's reign, Confucian thought gradually replaced Legalist thought; Confucian scholars were welcomed into his government, while the harsh Legalist laws were lessened. Emperor Gaozu's efforts laid a solid foundation for the over four-hundred-year reign of the Han Dynasty.

Liu Bang also devoted to subduing the unruly kings . He soon annexed most of the kingdoms and established princehoods, with his sons and relatives as princes. By doing so he consolidated his new-born empire.

Liu Bang tried military solutions against the Xiongnu ( 匈奴 ) but was beaten hard in the battlefield. He then decided to appease the Xiongnu by marrying ladies from royal family to Chanyu , the leaders of the Xiongnu . This policy would not change for about 70 years.

Liu Bang was treacherous, bold and arrogant. These being said, he knew how to manipulate his peers and subordinates. He bid them glory and territories generously when he was fighting Xiang Yu , which won the hearty support of most of his peer kings and subordinates. However, once he became the emperor, Liu Bang ruthlessly oppressed them and killed several of them, most notably Han Xin ( 韩信 ) , Peng Yue ( 彭越 ) and Ying Bu ( 英布 ) .