Thráin I (Third Age 1934 – 2190, died aged 256) was the King of Durin's Folk for 209 years, succeeding his father, Náin I, when he was killed by the Balrog in T.A. 1981. Thráin founded the Kingdom under the Mountain at Erebor, and was a descendent of Durin the Deathless via his grandfather Durin VI.
Thráin's grandfather, Durin VI, was King of Khazad-dûm when the Balrog of Morgoth appeared in Moria; this Balrog has forever been known as Durin's Bane as Durin was killed by it in T.A. 1980. Durin's son - and Thráin's father - Náin I was then King. He attempted to hold out against the Balrog but was himself killed in 1981, being the last true King of Khazad-dûm until Durin VII and Last in the Fourth Age.
Thráin - at the tender age of 47 - became King of Durin's Folk. He led his wandering people until T.A. 1999 when he founded the Kingdom under the Mountain in Erebor. In Erebor the Dwarves began building a mighty kingdom, discovering the prized possession of King Thráin: the Arkenstone, the Heart of the Mountain. 
Thráin died in T.A. 2190 at the age of 256 and was succeeded by his son Thorin I. With a rule of 209 years, Thráin I was the longest-ruling of all the known Kings of Durin's Folk with, perhaps, the only exception being Durin the Deathless.
Other versions of the legendarium
It is not clear whether Thráin I existed in Tolkien's mind while he was writing The Hobbit or whether he was invented later, when writing the back-story of Lord of the Rings. The phrase on Thrór's Map "Here of old was Thrain - King under the Mountain" causes some fans (like Michael Martinez) to claim that Tolkien wrote it for Thráin I, since Thráin II was never a King under the Mountain.
Christopher Tolkien and Douglas Anderson and John Rateliff mention that Thráin I was invented later. In that case, Tolkien had made a mistake while drawing the Thrór's Map, which was retconned later with the introduction of an older Thráin.
- ↑ 1.0 1.1 1.2 J.R.R. Tolkien, The Lord of the Rings, Appendix A, "Durin's Folk"
- ↑ Chester Nathan Gould, "Dwarf-Names: A Study in Old Icelandic Religion", published in Publications of the Modern Language Association of America, Vol 44 (1929), issue #4, pp. 939-967
- ↑ J.R.R. Tolkien, The Hobbit, "Thrór's Map"
- ↑ A History of Thrain(s) in The Hobbit
House of Durin
|King of Durin's Folk|
T.A. 1981 - 2190
|1st King under the Mountain|
T.A. 1999 - 2190