Dáin II Ironfoot was a Dwarf and king of Erebor in J. R. R. Tolkien’s high fantasy legendarium concerning Middle-earth. His story is told primarily in Appendix A of The Lord of the Rings, and he appears briefly in The Hobbit.
Dáin, one of the Dwarves’ greatest warriors, was the son of Náin and grandson of Grór, the youngest son of Dáin I of Durin’s folk. Following his father’s death, Dáin became lord of the Dwarves of the Iron Hills in Wilderland; and after the death of Thorin Oakenshield and the extinction of the main branch of Durin’s line, he succeeded Thorin as King under the Mountain and King of Durin’s folk, the first not in the direct line.
Dáin’s father, Náin, was killed by the great Orc Azog during the Battle of Nanduhirion before the gates of Moria, the culmination of the War of the Dwarves and Orcs. Dáin avenged Náin, slaying Azog in single combat. He was a very young Dwarf at the time (only 32, while Dwarves reach maturity, or “battle-readiness” at the age of 30), and this was heralded as a magnificent feat. Dáin alone looked past the gate into Moria, saw that the Balrog was still active within, and knew that it was impossible for the Dwarves to return at that time. He dissuaded Thráin II from attempting to occupy Moria.
Dáin was second cousin to Thorin Oakenshield, and responded to Thorin’s call for help during the quest to reclaim Erebor. Dáin set out with several hundred Dwarves, and arrived just in time for the Battle of Five Armies (as recounted in The Hobbit). Thorin was mortally wounded in this battle, and Dáin became king after his death.
Dáin was killed during the War of the Ring in T.A. 3019, defending the body of his ally King Brand of Dale before the gates of Erebor. He was by then an old Dwarf – aged 252 according to Appendix A in The Lord of the Rings – but his prowess in battle was still great. After the war he was succeeded by his son, Thorin III Stonehelm.
Though it is unclear whether he knew it, Dáin lived just long enough to see the way cleared for the Dwarves to retake Moria; he died just weeks after Gandalf’s defeat of the Balrog early in T.A. 3019.