Various upanishads attack the same issue (of creation and creator) from various angles, because there is no singl eprecise way of expressing it.
One Upanishad says, in the beginning, there was only God and nothing else. A thought arose in him, "May I become many?". And, so he spun out of himself this entire world of myriad forms, just as a spider spins a web out of itself!
The question, "who created the creator", does not arise, because the definition of creator is that omnipotent, omnipresent entity, whom nobody created.
Nobody created him, he was always there, and he will always be there and he is eternal.
