The Old Prussians or Baltic Prussians (German: Pruzzen or Prußen; Latin: Pruteni; Latvian: Prūši; Lithuanian: Prūsai; Polish: Prusowie) were an ethnic group, autochthonous Baltic tribes that inhabited Prussia, the lands of the southeastern Baltic Sea in the area around the Vistula and Curonian Lagoons. They spoke a language now known as Old Prussian and followed pagan Prussian mythology.

During the 13th century, the Old Prussians were conquered by the Teutonic Knights, and gradually assimilated over the following centuries. The former German state of Prussia took its name from the Baltic Prussians, although it was led by Germans who had assimilated the Old Prussians; the old Prussian language was extinct by the 17th or early 18th century.

The land of the Old Prussians consisted approximately of central and southern East Prussia — the present-day Warmian-Masurian Voivodeship of Poland, the Kaliningrad Oblast of Russia, and the southern Klaipėda Region of Lithuania.

The names of the Baltic Prussian tribes all reflected the theme of landscape. Most of the names were based on water, an understandable convention in a land dotted with thousands of lakes, streams, and swamps (the Masurian Lake District). Indeed, that landscape caused the very partial isolation that preserved the Baltic language group as the most archaic in Europe. To the south, the terrain runs into the Pripet Marshes at the headwaters of the Dnieper River; these have been an effective barrier over the millennia.

Song In (in hangul 송인, in hanja 宋仁) was a civil official in the mid-Goryeo era who became the intermediary founder of the Jincheon Song clan. His highest post was munha pyeongjangsa (문하 평장사). This was the highest government position in the period. Song In was responsible for administration, judicial affairs and economy in the district.

As he performed meritorious deeds during the King, he was conferred with Chanhwagongsin and Jincheonbaek. Baek was a position of politicians who were responsible for administration, judicial affairs and economy in the district. As the government created him Jincheonbaek, his family started regarding Jincheon as their origin. Hence, the family origin became Jincheon Song.

When he was in the position of Sangsanbaek, he tried to be just and fair in all the administrative affairs and strived to enhance the welfare of his people. He also focused on education for the youth and courtesy for people, which made his district famous for most excellent behaviors in the nation. After that, the people have long paid tribute to his feats.