Okay, so what we know about the Shade Lord is mainly due to Godhome/Godseeker dialogue. To quote Godseeker: “Shame beyond shame! We failed to perceive such obvious truth. Punish us, o Devourer! Crush us! Rain nail and lash on Our pathetic being. We welcome such divine vengeance!”, while speaking to the Knight, talking as though the Shade Lord was/is some vengeful and angry god, a force of destruction and wrath. The ancient void civilization, just like Godseeker, worshipped the being. While they seem to see it as this almighty god, everything else in the game treats it like a demon, Hallownest's devil. But when the void civilization died out, it seems the Shade Lord was forgotten after a while, resulting in it returning to a shapeless form, with only animalistic instincts fueling it, it seems. I believe that The Knight is the direct reincarnation of the Shade Lord. Our player character is shown to have more of a connection to the ancient being than any other being, including other vessels. When the Pale King made the vessels, they were all given the power of void. But, only the Knight seems to be able to do certain things. They are shown to be able to mix soul spells with their own void abilities, making them stronger. The Pure Vessel, who is meant to be thye strongest of all the vessels, couldn't even do that, and was only shown using void tendrils in one of their moves. The Knight has been shown to do that, and more. How we obtain Void heart also adds to my theory; the Knight confronts the void, remembering and accepting the circumstances of their own birth, and coming to terms with any trauma left by the Pale King. When we obtain Void heart, it is stated that the Knight "reunited the void", and all void-based enemies stop attacking us, even though all the other vessels still have unresolved trauma, therefore are not "reunited" like our player chracter. Our own shade, the siblings, they all stop attacking us, as if they see us as something beyond them, almost like we're royalty to them. During the final fight with the Radiance, she refers to us as "...ANCIENT ENEMY...", so The Radiance clearly knows we are composed of void. In Pantheon V, the void rises to the heavens, and it is the Knight who descends into the void before the Shade Lord appears, implying it was a sort of transformation, or ascension to true divinity. To furthur this, the statue of the Knight in Godhome turns into a statue of the Shade Lord, with the text, "Void given focus", as though it was not just given shape, but intentionally focused into a specific form. To add, the King soul charm is the charm that becomes Void Heart, going back to the quote from the Pale King, "born of god and void", a charm made by gods, consumed by the power of void. The charm is stated to become a part of the Knight, as well, shedding the paleness, and becoming something far stronger. Another thing about Godseeker's dialogue, is that they seem to see us as scum, lowest of the low, as if we were a monster/demon, which is what the Shade Lord is usually described as. It is only when the light is consumed, that they refer to us as "the god of gods". By the end of the game, we didn't just reunite the void, but reunited OURSELVES. And then, to add, the last time we see the Knight, the "Sister of The Void" ending, where we see flashes of the Shade Lord in the Knight's place, furthering this deep connection between these two chracters. Not to mention, if the Shade Lord was this force of nature as it is described, it would not have ever bothered to save Hornet, but it did, because that isn't the Shade Lord. The Knight cares about their sister, proven by Winged Nosk taking the form of Hornet, and as we know, Nosk takes on the form of loved ones to lure victims in. The Shade Lord is long dead, but reborn as the Knight. The Shade Lord we see in the game is not the original, but a manifestation of the Knight's potential being realized to the fullest extent, as the Knight takes on the physical form of their past life. This could very well be false, but I have been thinking/speculating about void for a good minute