This is a common misconception quoted by atheists.
God does not exist in time, so there can be no concept of who or what created God.
God created time.
This is a common misconception of theists who
don't think about their silly assertions. Time has nothing to do with it. One could say, from the point of view of general relativity, that "the space-time manifold does not exist in time, so there can be no concept of who or what created the manifold. It contains time". See?
Asking the question of why something exists, rather than something else or nothing at all, can be applied just as well to any god you postulate as it can to the universe.
This is why
making up a god explains exactly nothing fundamental at all. It just moves the questions around a bit. You think the universe is, in some way, improbable, then so is any god. You think the existence of the universe requires explanation, then so does the existence of any god.
This goes right back to the point I keep make and you keep on ignoring. Adding an evidence-free creator inevitably makes things
more improbable. You've just added to any improbability you're trying to explain.
It's a giant leap in the wrong direction.
A god cannot explain complexity or improbability. Claiming them as evidence for a god is trite, simplistic thinking.