Hardly any question is asked more often. The short answer is: no one. For the question presupposes that the Creator was created — yet the First Cause can have no beginning, otherwise it would not be the first. Why this is not an excuse but a logical necessity is shown in Station IV of the journey. It builds on the insights of Stations I to III: the universe must have a beginning, and only an almighty Creator comes into question as the First Cause. You can read the answer here word for word, exactly as it appears in the journey.
Now that we have absolute certainty that only a Creator can have created the universe and human beings, the following question arises:
What properties must the Creator possess in order to create an entire universe out of nothing?
The Creator must be necessary and independent
Everything we see in the world depends on something else in order to exist. The first cause, or the Creator, however, can depend on nothing and must necessarily exist. Consider, for example, an author and a story. The story depends for its existence on the author. If the author did not exist, the story would not exist either. The existence of the author, however, does not depend on the story. He exists whether he writes the story or not. In this context the author thus represents a necessary existence, while the story represents a dependent existence.
Outside of this context, the author, like everything else in the universe, is dependent and was caused by something. Only the Creator is a necessary existence. He is independent and must necessarily exist, like the author in the example. Otherwise the universe and human beings would not exist. Someone must have knocked over the first domino.
The first cause must be eternal
Since the first cause must necessarily exist, and its non-existence is ruled out, it can only exist beyond time and space. The Creator of the universe can therefore have neither beginning nor end. He must be eternal and have caused everything else.
The first cause must be simple and cannot consist of parts
If something consists of parts, like a tower made of stones, then it needs someone to join these parts together. That is, a tower depends on stones being present and on someone stacking them upon one another.
The Creator cannot consist of several parts. For if he consisted of parts, someone would first have to assemble these parts. And then that would be the truly first cause. Therefore the Creator must be unique and simple. He needs no one and cannot consist of parts.
The first cause must be almighty
Our Earth fits into the sun about 1.3 million times. The observable universe contains around two trillion galaxies. On average, a galaxy has about a billion stars. That makes roughly two sextillion (2 × 1021) stars in total. All of this came into being out of nothing. This requires an unimaginable power. Therefore the first cause must be an almighty Creator, who not only created everything but also keeps it running through perfect laws and order.
The first cause must have a will
Since the universe came into being at a particular point in time, this means that the Creator decided at a particular point in time to let it come into being. This shows that the Creator must have a will.
On the basis of pure logic, then, we can clearly conclude that the first cause must be an eternal, necessarily existing and almighty Creator.
So the Creator was not created — he is the Uncaused, without whom nothing would exist. A related question is answered in the second part of Station IV: Could there be multiple gods?