I'm not referring to how to beat Seath or how to find him, as this question has already been discussed in great detail.
However, I still find this to be the most mysterious canon in all of Dark Souls.
As far as I know, the only actual piece of dialogue that talks about Seath is one sentence, right at the beginning of the game –
"And Seath the Scaleless betrayed his own, and the dragons were no more"
Has anyone dug up any evidence to the following?
- How did Seath betray the dragons?
- Did he lose his scales before or after slaying the dragons?
- Is there any connection between Priscilla and Seath, other than the fact that she's almost definitely his daughter due to the fact that Seath is the only albino dragon in the whole cannon (Who is her mother?)
- How did Seath become cursed?
- Why does he live in the Duke's Archives? (It's been suggested that Seath is the Duke)
Best Answer
CrystalBlue's answer provides a good rundown of what we know about Seath in confirmed canon- though I should note that I don't believe it is confirmed that Seath is Priscilla's father. It seems extremely likely and the community tends to take it for granted, but it is not actually confirmed in-game.
EpicNameBro runs down what we know (canon) and suspect (non-canon) about Seath in his Dark Souls Lore series (skip to 3:44):
Essentially, he's one messed up dude, much like most of the Dark Souls cast. It's believed that he betrayed the other dragons because of jealousy, but the nature of his betrayal is unknown- ENB puts forth the idea that Seath stole the Primordial Crystal from the other dragons, which allowed them to be killed by Gwyn and the other Lords. Some believe rather that the crystal was made by Seath in his experiments (though the title 'Primordial' seems to contradict this).
Something that Seath learned in his archives while studying immortality drove him to insanity; the same thing happens to Big Hat Logan if you let him poke around inside the archives enough. Again, this knowledge seems to have something to do with crystals.
It's interesting to note that, at the time you meet him, not only is Seath scaleless and colorless but also sightless and legless. It's unknown which of these mutilations he was born with, and which of them were caused by his research. Personally, I think that he was born with all of them, going mostly off his appearance in the intro cinematic. His body is partially covered with crystals, however, and this is clearly something that happened to him after he started experimenting with them.
On the subject of Priscilla: Again, ENB goes over this in the video, but the main reasons that people believe Seath is Priscilla's father are:
-They're both albino.
-Priscilla lives in the Painted World, a place where forsaken people/objects/magic go. Being the spawn of a dragon (who's pretty freakish himself) and... something else... would definitely make you fall into this category.
-Seath had a thing for capturing maidens. I'll let you fill in the blanks.
-Like you said, there doesn't seem to be many other candidates, especially since Seath is the only dragon known to have lived (at one point peacefully) close to civilization.
If Seath is Priscilla's father, than that makes pretty much any humanoid (not really human, the people of Anor Londo were more like gods) female a candidate. Gwynevere herself is sometimes considered, along with all of the handmaidens of hers that Seath kidnapped.
(Personally, I can't help but wonder if Seath would even be capable of fathering an offspring. He doesn't have any legs, and he's pretty mutated in almost every other way. Eh. Just a thought.)