The idea behind this question is that if you say that God created the universe, you must then ask who or what created God. For every cause must have a prior cause. Atheists come up with this challenge sometimes, thinking they have thereby undermined the thought processes of the religious believer, but it actually shows their inability to think metaphysically. Who designed the designer is a meaningless question because it doesn't recognise the difference between spirit and matter. That is to say, between something that exists in time and space, and something that just exists. God is existence itself and therefore absolute being-ness. He needs no design because of his perfect wholeness and oneness. He is not caused because he is not a thing. He just is. And if it is asked how something perfectly simple can be intelligent, the answer is that God does not think. He knows. His being is his knowing, instant and complete.
The material world is one of cause and effect, and when I say the material world I mean the created world so not just physical matter. This is the world of time and space, movement and change. But the spiritual world or state that gave rise to this is not subject to time or space or movement or change, and so notions of cause and effect do not apply to it. This is why certain ancient teachings can say that being came from non-being. I would prefer to express this as becoming came from being but it amounts to the same thing. The world of cause and effect came from uncaused being. Who designed the designer is a question that can only apply to the world of material existence. It has no meaning in a spiritual world which exists outside time.