The Deathless

After the Elves had awoken, the first of the Dwarves also awoke from their long sleep. Durin was the eldest of the Seven Fathers of that race, and it was he who discovered a network of caves in the Misty Mountains above the lake of Kheled-zarâm, and there founded the great Dwarf-city of Khazad-dûm. There he ruled for an astonishingly long time, so long indeed that he became known as Durin the Deathless. In fact he was not deathless: he died before the end of the First Age, and was entombed within Khazad-dûm.

As the Ages passed, the Dwarves believed that Durin would return at times, reincarnated among his descendants, or at least that Dwarves would be born so like the original Durin that they were given his name. There were six of these descendants of Durin in total; according to legend the last of them reclaimed Khazad-dûm and ruled there as his ancient ancestor had done.

It's also hinted that the Dwarves thought that the original Durin was merely 'sleeping', and would somehow return in the far future. The details of this tradition are unclear, but Gimli's song of Khazad-dûm says: 'There lies his crown in water deep, till Durin wakes again from sleep' (The Fellowship of the Ring II 4, A Journey in the Dark). Since Durin's Crown was made up of stars reflected in the water of Kheled-zarâm, this seems to imply that Durin was not expected to return until the unmaking of the world.