Well little one, the idea of a "king of the universe" is just a really big imaginary concept that some people believe in. It's like a make-believe story where someone has all the power and control over everything that exists.
Think of it like a game of pretend where you are the king or queen of a kingdom. But instead of just ruling over a small kingdom, this imaginary king or queen would rule over everything in the entire universe.
Of course, in real life, nobody can actually be the king of the whole universe because it's just too big and complicated. But for some people, believing in this idea can make them feel happier and more secure. They believe that this imaginary king or queen is looking out for them and making sure that everything in the universe is working out okay.
It's important to remember that this is just a story, like a fairytale, and nobody actually knows what's really going on in the universe. The best we can do is keep exploring and learning more about all the amazing things that are out there.