Is Kris the Knight? At face value, this seems insane. Right? Well, let's look at the evidence.
First and foremost, the Knight opens Dark Fountains. Now, what does Kris do at the end of Chapter 2? They create a Dark Fountain.
Second, what does Kris look like in Dark Worlds? That's right, a Knight.
This is what Kris looks like in a Dark World, they're wearing plated armor. They even have a sword.
We know that Kris made a Dark Fountain at the end of Chapter 2, so is it really that far off to assume that they also made the one in the library's computer lab? Or the on in the closet for that matter. Well, we know that they had their knife at the end of chapter 1, and only Toby Fox knows what they did before chapter 1.
In the end of chapter 2, they rips they soul out before creating the new fountain, and shuffling around outside; and slashing Toriel's tires. In fact, they rips out their heart in the end of chapter 1, too. Afterward, they presumably went to library and made a fountain in the computer lab.
This is a really common theory, but it really needs more evidence to be collected, and more speculating to be done.
Image taken from Fandom.
Quick note from 2024: I'm aware of the design of Kris from that rodeo teaser. I'm pretty much keeping this up for historical reasons at this point. Encase you're wondering, here's Kris' design from there:
