This question assumes that everything must have a cause. While it is true that everything that begins to exist requires a cause, God did not begin to exist. He is eternal and uncaused. Asking “Who created God?” is like asking “What is north of the North Pole?”—it is a category mistake.
Philosophically, an infinite regress of causes is impossible. If every cause required another cause before it, we would never arrive at the present moment. There must be a first cause that itself is uncaused. Christianity identifies this uncaused cause as God.
Science supports this reasoning. The Big Bang shows the universe had a beginning. Space, time, and matter came into existence. Since the cause of the universe must be outside space, time, and matter, it must be timeless, immaterial, and powerful—attributes consistent with God.
Far from being an arbitrary answer, God as the eternal Creator is the most rational explanation for existence. Every contingent thing points to a necessary being. Christianity proclaims that this eternal God has revealed Himself personally, not as an abstract force but as the living Creator who loves and redeems.