Sua origem não é totalmente conhecida.
Esta fonte declara:
Tolkien clearly wrote that dragons were bred by Morgoth but no one is sure how. Some belief that dragons are embodied Maiar, others believe they are simply beasts who were trained by Morgoth to speak and to think, still others suggest they are "sparks" of Morgoth himself, another theory is that dragons are crossbred from balrogs and other beasts
Os dragões são conhecidos por serem imortais, poderosos, inteligentes, mas também gananciosos.
Outra teoria sobre seus estados de origem:
The theory that Dragons were simply beasts perhaps physically enhanced by Morgoth, such as corrupted eagles is a very popular theory.
Existem dois tipos de dragões:
- Cold-drakes
- Dragões de fogo (Urulóki)
Há também outro terceiro tipo, Long-worms, sem asas.
Cold-drakes foram usados para criar drakes de fogo, mas origem dos Cold-drakes não é conhecido :
Tolkien gives no hint to the history of the cold-drakes after this time period. They may have, however, been animals created by Yavanna (and therefore the first dragons) that were then used by Morgoth to breed the much stronger and more wicked Uruloki.
Smaug é um dos bombeiros :
Tolkien confirmed in a letter that Smaug was the last of his kind (The last of the great Fire Drakes of Middle Earth...
Por esta declaração podemos concluir que Smaug foi criado por Morgoth.
Mas há outra coisa (de Fire-drakes ):
All the famous dragons throughout the ages were fire-drakes (aka Ancalagon, Glaurung, Smaug, etc.) although only some of them fought for Morgoth
Então nem todos lutaram por ele, mas todos foram aprimorados por ele (ao que parece).
Mais explicações para a aparição do Smaug na Terceira Era, Fire-drakes :
All Fire-drakes were thought to have been killed before the Second Age, but Smaug the Golden survived and in the Third Age descended on Erebor in TA 2770 and sacked the Lonely Mountain, at the time held by Thrór, the Dwarven King under the Mountain.