According to Samguk Sagi, a prince from the Buyeo Timur kingdom named Jumong fled after a power struggle with another prince in the kingdom, and he founded a kingdom named Goguryeo in 37 BC in an area called Jolbon Buyeo. It is presumably now located in the middle of the Yalu and Tung-chia valleys on the border of North Korea and Manchuria. Some historians believe that Goguryeo may have been established earlier, ie, in the 2nd century BC. In the ancient Chinese history book, Han Shu, Goguryeo said in Chinese script was first written in 113 BC when it was a small country under the control of Xuantu district. In the records of the Ancient Book of the Tang, it is mentioned that Emperor Taizong of the Tang Dynasty mentioned that the history of Goguryeo approaches 900 years. In 75 BC, a group called Yemaek, thought to be an original element of Goguryeo, attacked Xuantu District from the west of the Yalu river valley.
However, from written evidence from the Tang history books, Samguk Sagi, Nihon Shoki and so on tend to favor the year 37 BC or the middle of the 1st century BC for the establishment of Goguryeo. Proof of archaeological objects may support the existence of the Yemaek tribe in the 2nd century BC, but there is no direct evidence to explain whether they call their group Goguryeo. The first mention of the word Goguryeo as a group linked to the Yemaek tribe can be found in the references in Han Shu that tell the Goguryeo rebellion of AD 12, when they escape from Xuantu's influence. At this very moment the Goguryeo leaders began to change their titles to the title of Chinese leader, wang.
At its founding, the possibility of Goguryeo is a combination of Buyeo and Yemaek people. The Chinese Babad San Guo Zhi mentions in the section entitled Notes on Barbarians from the East, mentions that the Buyeo and Yemaek tribes are ethnically related and speak the same language. Nice history @slowwalker