The primordial serpents of Dark Souls: there is something under the surface
Kingseeker Frampt and Darkstalker Kaathe are two characters that I would define as quite nebulous. Only appearing in person in Dark Souls 1, their presence nonetheless is felt even in future installments. But what exactly is their deal? It's a rather difficult question to answer, for a simple reason: they can't be trusted. At all. This post isn't gonna be a sort of unified theory on who the serpents exactly are: however I'll try to compile most of the information we know and can infer about them and why there's way, way more to them than what meets the eye. Waaaaay more. Yeah this is gonna be a long post. VERY long. But, in my humble opinion, quite thought provoking. Disclaimer: probably not all of the following was intended by the writers. But you know, death of the author and all. I think it's fun to speculate and create meaning even where there might be move.
That said, let's start with the Serpent Species.
Besides Frampt and Kaathe, the Dark Lord ending of Dark Souls 1 (which we'll get back to later) shows us a large number of Primordial Serpents, so we can assume that there's a whole species of them. Maybe. It's never brought up again. Nonetheless, there are several things we can infer about the Serpents in general, or World Snakes as they're known in japanese.
First off, presumably, they're ancient. Duh. How ancient? From the age before the First Flame, possibly. In Dark Souls 3, the description for the Covetous Silver Serpent Ring reads as follows:
A silver ring depicting a snake that could have been, but never was, a dragon.
Interesting. So snakes (or at least some of them) are some sort of imperfect, malformed dragons. Additionally, Dark Souls 3 shows some statues depicting a more humanoid version of the Serpents, of which we can ordinarily only see their heads. Considering their depictions are very different to each other, I'm assuming it's just an artistic interpretation and the sculptors didn't actually know what they looked like. However, one should note the locations of these statues: the Grand Archive (probably connected to Seath's Duke's Archives) and the Ringed City ("gifted" by Gwyn to the Pygmy Lords).
Now, let us talk about Frampt.
That Kingseeker Frampt is lying to you isn't exactly a groundbreaking fact. After all, this close confidant of Gwyn is in cahoots with him regarding the prophecy of a Chosen Undead, a made up folk story to get some poor undead bastard to throw themselves in the fire in order to kindle it once needed. This is all bullshit obviously, there's no such thing as the prophecy and the kindling of the fire is an unnatural sin performed by Gwyn. This means that Frampt is manipulating you with incomplete information in order to get you to link the Flame. One would assume that this would be his ultimate goal.
Or is it?
There are several odd things about Frampt.
For starters, as mentioned before, the Dark Lord Ending. In it, when you refuse to link the fire, Kaathe (we'll talk about him later) makes a point to say that both he and Frampt will now serve you. Why would Frampt do that? You could speculate that he's bound by some sort of oath to the Dark Lord, perhaps because of his nature as a quasi-dragon born in the dark. This could maybe explain the statue of him found in the Ringed City. But by this point, everyone that could be considered his "superior" is dead, and I'm not sure why he would have any obligations to serve you: if he feared being killed by the Dark Lord, well, he could just hide. Perhaps his oath is more fundamental, and he can't go against the Dark Lord because of the very nature of his being. Maybe he allied to Lord Gwyn to try and break this shackle? Perhaps. But I suspect, once again, that there's more to it.
Let's take a look at a very strange mechanic: feeding Frampt.
In Dark Souls 1, you can feed certain items to Frampt, and he'll pay you back with souls. Usually this is not really worth it, because he undervalues items a lot. However, here's the curious thing: for some items, he will only give you a meager 1 soul, while for others he will reward you with a bounty much higher than the value of the item. This is not a mistake, it's hardcoded in, so hey, it should have some significance. Let's look at these outliers.
Frampt will give you 1 soul for anything that has to do with either Seath the Scaleless or Smough; conversely, he will reward you handomely for anything that has to do with Gwyn (soul included), Gwyndolin (soul included), the Moonlight Butterfly, Dragons, Queelag and, funnily enough, women armor sets. So huh, let's unpack this.
It's the women's clothing, believe it or not, that provide some insight. Given that he pays you more for it, I'm assuming that he gives you more souls as a reward for bringing him that item. Either that or he's a misogynist, but I'm more leaning towards horny. And certainly the Soul of Gwyn, the one he pays you the most for, fits: your objective was to kill the crazed Gwyn, and his Soul proves that you've done it. You can't actually feed him it without going to ng+, but hey, it's a technical limitation
With Gwyndolin things start becoming a little bit strange. To have his Soul, you must have killed him. This is a problem for a few reasons: first off, it's his best friend's son. Why would he be happy about you killing him? Secondly, killing him means dispelling the Anor Londo illusion, meaning finding out that the Gods, and him, are lying to you. Now why would he be ok with you knowing that?
The Moonlight Butterfly is a bit strange, since it was created by Seath, but it seems to be connected in some way to Gwyndolin (the moon theming plus the same music). I don't think it's terribly relevant anyway.
Queelag, I have no clue about, epecially considering the fact that he gives no special reward for the Soul of the Witch of Izalith. It could either be because she's guarding the second bell of awakening or because she's hot. Probably cause she's hot.
Now, let's look at a strange thing. He gives nothing for Seath but a lot for the Dragons. Seath betrayed the Dragons, so this is relevant. But how? If he dislikes Seath, this would imply that he's on the dragon's side. But this cannot be, since the dragons and Gwyn are enemies. Maybe he just likes to consume dragon items in an attempt to become a full fledged dragon: this would also be strange considering his allegiance. Maybe he just enjoys eating dragon items but dislikes the taste of Seath (who is physiologically pretty different from other dragons). This, however, would imply that he also enjoyed eating Gwyn and Gwyndolin. Which, frankly, I find the most likely possibility, with interesting implications.
As for Smough, let's be honest, he probably tastes like shit.
Let's move on to Kaathe.
Darkstalker Kaathe seems to be, at the same time, more and less trustworthy than Frampt. More trustworty because he's the one to tell you about the lies of Gwyn, and the truth about the Dark Soul. And he's not lying to you about that. At the same time, he convinced the Lords of New Londo do embrace the Darkness, as well as the people of Oolacile to dig up the corpse of a Pygmy which didn't end very well.
Not much else is known about him: a somewhat obscure fact is that he considers Seath the Scaleless to be a traitor: so, it seems, he's aligned with the dragons despite not being one. What this says about the other Serpent is hard to tell.
However, one last thing is known about him. He wants to let the Flame die, and make the world turn back to an Age of Dark.
Or does he?
The Sable Church, helmed by Yuria of Londor, is an organization devoted to a single goal: usurp the Flame and bring forth an age not of Light or Dark, but of Hollows. This is different from an Age of Dark in several ways. First off, the Flame persists, but is claimed by an individual who is both Unkindled (that is someone who attempted to link the Flame but failed) and Hollow. In an Age of Dark, with the Flame gone, it is unclear what would happen: it is called many times "the age of humanity", but no one actually knows what humanity's original, primordial form is: for all we know, it could just be an existence spent in a formless void as wandering spirits.
At the same time, nothing says that it couldn't be an utopia: but the point is that you can't know, there is an impassable veil that hides its true nature until it happens. At some point some embers will reappear from the Dark again, and bring forth a new age of Fire. But will it be a good one? Who knows. In comparison usurping the Flame is much more straightforward: similar to the current Age of Fire, except it's Hollows that hold power and not Gods. It is not clear how sentient would Hollows be in such an age, considering their usual zombie-like behavior, but since hollowing is tied to Gwyn linking humanity to the Flame we can presume that something would change, otherwise it would be quite a shitty age and idk why they would pursue it.
There's another thing about the Sable Church. From item descriptions and dialogue it is evident that they worship none other than Darkstalker Kaathe, who appears to have perished since the first game (there's a theory I like about it but this post is already long enough).
Now hold on, hold on. Doesn't Kaathe want to bring forth an Age of Dark? Where did Frampt go in all of this? What is going on?
Let's take a step back. If Kaathe wasn't lying to the Sable Church (and I don't believe he is) then he was lying to you in the first game. Not an unlikely prospect, since Frampt was doing the same thing. But why try and get you to be the Dark Lord if what he was looking for was a Lord of Hollows?
First off let's establish something. No matter which ending you pick in Dark Souls 1, I don't believe that an Age of Dark ever happens between that game and 3. This is because there seems to be a linear continuity (somehwat) between the eras the game is set in, which wouldn't be possible if, well, the cycle underwent a big reset. So even if you become Dark Lord, something happens to stop a true Age of Dark from happening.
With that out of the way, here's what I think. When is the only time that a Lord of Hollows can arise? Only when the world is in shambles due to the strain of the artificial cycle taken to its extreme. How do you get to that point? By continously linking the Flame and making it fight the Abyss over and over, purposefully feeding the feud between Light and Dark that should have already ended long ago, slowly weakening the Flame until it is just barely able to hold on and the entire world has been burned to ashes. At that point the Lords of Cinders arise from their graves to link it again, and again and again, until even them refuse to do it. At this point, the Unkindled will rise: after an endless, purposeful cycle of stirring both the Flame and the Abyss.
Flame and Abyss. Frampt and Kaathe.
I want to show something, now. An interesting little design on an otherwise unremarkable shield. The caduceus round shield.
Two serpents heads, joined at the body. Now, is there any reason to presume that this shield is a true depiction of the nature of Frampt and Kaathe, some sort of bicephalous Ourobouros? Well, we don't know. It would certainly make some amount of sense, however. What I think is that, no matter how literally true this is, it shows at least metaphorically the relationship of the two Serpents. They're working together.
You're not the only undead that they contact, after all. Plenty more people, like you, in your world and parallel ones, are spurred by Frampt to link the Flame and by Kaathe to let it die. This is why neither of them particularly cares about you finding out the truth, or joining the other. You're just a disposable pawn in the grand scheme. When a Dark Lord arise, they pretend to worship them, only to betray them at the last second, getting someone else to kindle the Flame and keep the cycle going. Over, and over again. Till the Unkindled finally rise.
There are, of course, some open questions. Why do they want an age of Hollows to come to pass? Perhaps it is linked to their complicated relationship with dragons: after all, they're only incomplete dragons, and they would hardly have a place in an Age of Dark. Perhaps it has something to do with a promise made to the first Pygmies. Or then again, perhaps to defend against them. And then, what about the other Serpents? Are they working with them? Are they from other worlds? Are they all joined in some sort of giant eldrich hydra, its true body hidden from sight?
It is all very complicated, frankly. We probably will never know the true motives of the Serpents, as well as their nature: however, what I hope this analysis has made clear is that there is much, much more under the surface than what it seems like. Like their body. That's literally under the surface.
Me when other people point out the serpent on the caduceus and say that it could depict Kaathe and Frampt:
The theory of them being either the same being or two heads sharing a body has always been one of my favorite theories.
You've got Frampt actively propping up this legend that seems designed to attract more and more powerful undead, but, as you point out, there's clearly something more going on.
If you ignore Frampt, then you get contacted by Kaathe. Even that feels almost like a test. You talk to Kaathe and he's basically like, "Fuck Frampt, that bastard doesn't know anything. But you, you're smart enough to see through the ruse. Let me tell you what's actually going on."
But then with the reading of them being the same person, it feels like Kaathe's explanation is just another layer of manipulation. I like your idea of them perpetually running this cycle just trying to weaken the First Flame enough to start an Age of Hollows.
Then there's the question about why the want an Age of Hollows. I think the answer may be as simple as it being the only way to actually effect a permanent end to the Age of Fire and Gwyn's influence on the world. I don't think the serpents really give a shit about humanity or the pygmies. I think they just despise Gwyn and want the world rid of him.
(My wife and I also have a crack-ier theory that Kaathe and Frampt are the two original beings and that each cycle is just them playing chess over and over. Kaathe wins, Age of Dark; Frampt wins, Age of Fire. The chess match is just whichever can manipulate the chosen undead better.)