The Nangchen royal family belonged to the Dru ('bru) clan and ruled over a pastoral kingdom in eastern Tibet whose capital Jyekundo was one of the centers of trade in Kham. In 1240 the Mongol prince Godan Khan endowed a local monastery, Kumbum Monastery, which contained the reliquary of Tishri Repa Sherab Sengge, with an estate of tax-paying subjects and also sponsored the construction of Nangsochenmo Castle. A disciple of Tishri Repa called Trewo Alu became the secular leader of this region, soon to be called Nangchen after the castle. It was Trewo Alu's son Chokyi Gyeltsen who became the first Nangchen king in 1300. Under Nangchen jurisdiction were twenty five autonomous tribes, including the Nangchen tribe itself, known as the twenty five tribes of Yushul.