From Rigpa Wiki
Radreng (Wyl. rwa sgreng) or Reting Monastery was the first Kadampa monastery founded by the great master Dromtönpa in 1056. It later became Gelugpa. It is situated north of Lhasa in the province of Ü. The abbots of the monastery, the Reting Rinpoches often served as regents of Tibet under the Dalai Lamas.