- This page is about Thráin I, first King Under the Mountain. For the father of Thorin Oakenshield, see Thráin.
Thráin I was the son of Náin I, the last king of the Longbeards in Khazad-dûm. When Náin was slain by the Balrog that had killed his father the year before, Thráin became king of the Longbeards and bearer of the dwarf-ring Handórm. Thráin evacuated the last of his people from Khazad-dûm in 1981 of the Third Age, and in 1999 T.A. he founded the kingdom of Erebor.
Thráin, first King Under the Mountain, had dealings with the Ai-thúda, precursors of the Rohirrim. They were not all pleasant; Fram, lord of the Ai-thúda, made a gift of the teeth of Scatha to King Thráin, which was taken as an insult. Relations did not improve, and eventually the Ai-thúda relocated far to the south.