What is the biggest thing to ever exist in the universe?

Well, that's quite a philosophical and scientific question, isn't it? But if we're talking about physical entities in the universe, then the answer could vary depending on how we define "biggest." For instance, if we're talking about size in terms of volume, then the largest known object in the universe is a supercluster of galaxies, which is a collection of thousands of galaxies bound together by gravity. However, if we're talking about the largest known single object, then it's likely to be a quasar or a supermassive black hole, which are incredibly massive and dense, but much smaller in terms of overall size compared to a supercluster. But, of course, the universe itself is constantly expanding and evolving, so who knows what might be discovered in the future that could challenge our current understanding of what the "biggest thing" is.