Dáin is a character from J.R.R. Tolkien's Middle-earth legendarium, specifically featured in "The Hobbit." He is the King under the Mountain and a leader of the Dwarves of the Iron Hills. Dáin is known for his bravery and strength, playing a crucial role in the Battle of the Five Armies. In the story, Dáin arrives to aid Thorin Oakenshield and his company of Dwarves after the death of Smaug, the dragon. He becomes the rightful king of Erebor after Thorin's demise, ensuring the prosperity of the Dwarves and their allies in the aftermath of the battle.