The first Taishang Huang (retired emperor) in Chinese history was Li Yuan, the Gaozu Emperor of the Tang Dynasty. In the year 626 AD, Li Yuan's second son, Prince of Qin, Li Shimin, laid an ambush at Xuanwu Gate and killed his older brother, Li Jiancheng, and younger brother, Li Yuanji, while they were on their way to court. At this time, Li Yuan was boating leisurely on the inner lake of the palace when suddenly a group of soldiers rushed to him, claiming that they were ordered by Prince of Qin to protect His Father the Emperor. Upon hearing the news of his two sons' death, Li Yuan was panic-stricken. He had just been emperor for nine years and was still indulging in being an emperor. But he clearly knew that the court situation had already been under control by his second son. Therefore, he had no choice but to issue an edict to abdicate and announced that Li Shimin would succeed to the throne. Li Shimin wanted to be the emperor, but on the other hand, he didn't want to bear the notorious name of forcing his father to give up the throne. Then his strategists gave him an idea: let his father be the "Taishang Huang" to preserve the dignity of his father. It can be said that Li Shimin was the first person who came up with the concept of "Taishang Huang". Li Yuan spent 10 years as a retired emperor and died in depression in the year 635 AD.