Who was Durin the Deathless?
The first Durin also known as Durin the Deathless, of Khazad-dûm was the oldest of the Seven Fathers of the Dwarves and created by the Ainur (the Holy Ones) Aulë.
According to the myths, Durin was set to sleep beneath Mount Gundabad in Middle-earth until the Elves awoke. Upon his awakening in the Years of the trees, he traveled until he came upon a small lake in Azanulbizar named Mirrormere.
He created the great city within the Misty Mountains (Khazad-dûm), known by others as Moria.
The name Durin was taken from Old Norse. Many Dwarvish names were in the language of Dale, later translated in old Norse in The Hobbit and The Lord of the Rings. The name Durin was therefore the name of the first of the Seven Fathers of the Dwarves.
Why was he Deathless? Durin was called the Deathless because he lived far longer than any other known dwarf. Some believed he would be reincarnated six times, each time as a descendant of an older Durin.