The son of KingDurin VI of Khazad-dûm, who became King after his father was slain by the Balrog known as Durin's Bane. Náin's kingship lasted only a year, before he too was slain - his son Thráin I led the remnant of Durin's Folk away into the north.
Notes
1
'Náin' follows the form of the Old Norse dwarf-names like 'Thráin', but it isn't clear whether Old Norse is actually the source of the name in this case. It may be relevant that nain is the French word for 'dwarf', a fact that Tolkien must certainly have known. It is isn't clear whether this correspondence is intentional, or merely a bizarre coincidence.