But when it comes to the King of all Kuiper Belt objects, none of these little monsters can stake that claim. Because there's one object that we don't normally think of as a Kuiper Belt object that has them all beat. No, it doesn't qualify as a Kuiper Belt object; it's a planet, just like you've always learned. And in terms of atmospheric composition, it's virtually identical to the known worlds found in the Kuiper Belt. Even though it isn't currently in the Kuiper Belt, that doesn't stop it from being the largest, most massive, most accessible, first-discovered, and in many subjective ways, greatest Kuiper Belt Object of them all!