The Tang dynasty was founded by Li Yuan ( 李渊 ) who became emperor Gaozu ( 唐高祖 ) , the first emperor of Tang. He had defeated the armies of the declining Sui dynasty. In this he was actively and ably assisted by his sons, prominent among which was Li Shimin ( 李世民 ) , later emperor Tang Taizong ( 唐太宗 ) .

As the most capable and militarily inclined of Li Yuan's many sons, Taizong showed his promise at an early age, helping to rescue Emperor Yang from a Turkic ambush and besiegement at the age of 16. In 616, the 18-year-old Taizong followed his general-father to his garrison-post at Jinyang , Shanxi , where he instigated his father to stage a military coup against the autocratic and fast crumbling Sui regime. Leading the troops with his elder brother Li Jiancheng, the rebel army took the capital Changan in September 617, thereafter putting a puppet emperor on the throne before Li Yuan himself proclaimed the establishment of a new dynasty, the Tang, in 618.

After the establishment of Tang, Taizong was appointed the Prince of Qin ( 秦王 ) by his father. In the succeeding compaigns to augment the power of the new dynasty, Taizong made numerous contributions, intensifying the heated sibling rivalry between him and his two brothers—Li Jiacheng, the heir apparent, and Li Yuanji, a younger brother.

Taizong is credited with creating the custom of Door gods , colorful block prints and carvings placed by the doors of temples, homes, businesses, etc. to ward off evil spirits.

The original crown prince was Taizong's elder brother Li Jiancheng ( 李建成 ) although their father had promised the throne to Taizong more than once for his contributions to Tang. The situation was very similar to that of the Sui Dynasty where an ordinary crown prince would feel his future throne threatened by a more capable younger brother. Fearful of losing his throne, Li Jiancheng colluded with his fourth brother, Li Yuanji ( 李元吉 齐王 ), to get rid of Taizong. They attempted to poison Taizong during a feast and at another event urged him to ride a wild horse with hopes that he should fall. They also bribed Li Yuan's concubines to defame Taizong and tried unsuccessfully to lure his subordinates away with gold. Coincidentally, there was an Eastern Turk raid into Tang territory. Li Jiancheng recommended Li Yuanji to defend against this attack and used it as an excuse to summon much of Taizong's subordinates and soldiers out of his control. With much of Taizong's forces in Li Yuanji's command, Li Jiancheng plotted to assassinate Taizong in the farewell feast for Li Yuanji. However, Taizong was tipped of this plot and pre-empted it by ambushing and killing both Jiancheng and Yuanji at the Xuanwu Gate ( 玄武门之变 ) on July 2 , 626 . Jiangcheng and Yuanji on approaching the gate sensed danger and turned their horses to flee. Taizong himself led the pursuit and struck Jiancheng dead with an arrow. Taizong's horse then became frightened and ran towards a patch of forest where Taizong fell. Yuanji suddenly appeared and tried to strangle the unhorsed Taizong with a bow. Taizong's General Weichi Jingde then rode to Taizong's rescue and speared Yuanji. Jiancheng and Yuanji's forces still fighting at the Xuanwu Gate then ceased resistance upon being shown their leaders' heads. All of Jiancheng and Yuanji's sons were subsequently executed but all others involved were pardoned. Two days later, Taizong was made the new crown prince and regent (in that he would make decisions on all affairs and then notify the emperor). Two months later, Taizong's father Emperor Gaozu abdicated and he became emperor.

Taizong died in Hanfeng Hall of Cuiwei Palace in the year 649 ( 翠微宫含风殿 ) and was buried in August in Zhao Mausoleum . He was 50 years old.

A s the second emperor of the Tang Dynasty of China from 626 to 649 , Tang Taizong was considered to have been the co-founder of the dynasty. In 630, Taizong's General Li Jing conquered the once mighty Eastern Turkic Khanate and allowed Tang to become the major political and military power of the region. Accordingly, leaders of bordering tribes convened at Chang'an ( 长安 ) the same year and asked for Taizong to take on the title of Heavenly Khan ( 天可汗 ). Under his reign, the famous rule of Zhenguan ( 贞观之治 ) took place. At the time, it was said that there was no need for the people to lock doors at night and that items left on the road remain untouched by others. The prosperity of the era and the leadership of Taizong and his renowned officials epitomizes the peak of traditional rulership that future generations would strive to emulate.