A good question! One asked by both believers and unbelievers. The question was made notoriously famous by Richard Dawkins when he asked, if life and the universe is designed, then who designed the designer? Of course Dawkins asked this in order to show a flaw in theorizing God created everything, in that you can just as easily ask who created God? Or who created the thing that created God? Or who created the thing that created the thing that created God? It seems never ending…
Well, the universe is confined to the dimension of time. Time also had a beginning, as has been concluded by notable scholars such as Steven Hawking, George Ellis and Roger Penrose. The Bible also says time had a beginning as is described in Genesis 1. Time has, is and always will proceed forward, it cannot be reversed nor stopped. Any entity confined to that dimension must have a starting point and an end point. That entity must be created. Such an entity is all of creation whether it is the entire universe or just one human being.
The Bible says God is timeless, and resides outside the realm of time:
25 “All glory to him who alone is God, our Savior through Jesus Christ our Lord. All glory, majesty, power, and authority are his before all time, and in the present, and beyond all time! Amen.” Jude 1:25 (New Living Translation)
12 “But you, O Lord, will sit on your throne forever.” Psalm 102:12 (New Living Translation)
9 “For God saved us and called us to live a holy life. He did this, not because we deserved it, but because that was his plan from before the beginning of time—to show us his grace through Christ Jesus.” 2 Timothy 1:9 (New Living Translation)
It is clear from these verses that God is timeless. Therefore, God would only need to be created if He existed in the confined dimension of time. But since God is not confined to the restraints of time, then He resides outside of time, and is therefore not a creation. He is permanence; He has no beginning and end. Such an Entity would not require an additional creator. Therefore, God is not the product of something else, and has no creator above Him. Who created God? No one and nothing. He just IS.
 George Ellis and Ruth Williams, “Flat and Curved Space-Times.” (Oxford University Press) 1988.
 Penrose, R. 1966. “An analysis of the structure of space-time.” Adams Prize Essay, Cambridge University.
 Contrary to other religions, such as Hinduism which believes that the universe exists eternally with no beginning or end.