Board Thread:Lore Discussion/@comment-11923066-20130126013641/@comment-1852943-20130605125734

Whether Seath was breed directly from everlasting dragons or not, will forever be debatable (which I am quite enjoying btw!). The game content never specifies Seath as an everlasting dragon. In the opening sequence, it only says, "Seath the Scaless betrayed his own," which is open to interpretation. His Bequeathed Lord Soul calls him "the albino dragon," and the Moonlight Greatsword again calls him "the pale white dragon who betrayed his own." The White Dragon Breath spell created by Logan emits "crystal breath of Seath the Scaleless ... frightful power of the ancient dragons" which is the closest synonym I could find, however that again may be a reference to Seath's unnaturally extended lifespan and not specific to his breed.

Regarding breeds, I think it is safe to assume that any creature which drops a Dragon Scale or a Dragon Weapon can safely be considered a dragon-kin, since the item descriptions read either "Peeled from an ancient dragon," or "one of the rare dragon weapons," respectively. That would include the Hellkite Dragon, Gaping Dragon, Stone Dragon, Priscilla, Seath, Kalameet, the Hydras, and the Wyverns. All of them have vastly different appearances, and the only one who remotely resembles the ED in the opening sequence is the Stone Dragon (maybe Seath should have talked to him?).

Regarding Seath's reasons for betraying his own kind, that again is left to our speculation, but I am inclined to agree more or less with Lucky. Seath, lacking scales of immortality, may have become embittered towards the ED, jealous of the power he lacked. That type of negative energy can drive a character to commit otherwise unspeakable acts. Whether out of jealousy, spite, or cold logic, Seath would have much to gain by allying with Gwyn.

So far as I can determine, Seath's precise origins are as mysterious and debatable as Yoda's.