Assuming God exists, how did he come into existence?

In a nutshell: The question makes an assumption that It can not be proven that a creator exists. However using reasoning and rational thinking it can proven, in a few easy steps, that a creator exists and that he is eternal.  This question makes a couple of assumptions: it cannot be proven that God exists therefore it can only be assumed, and God's existence mirrors the known universe. The arguments that prove the existence of God have been well discussed and recorded; the two main arguments are intelligent design and the cosmological argument. The arguments for the existence of God are based on the mind through the use of reason and sense perception. The cosmological argument asks what are the origins of the known universe and everything in it? The universe and what it is comprised of can be sense perceived hence it exists, but what caused it to  come into existence? There are four possibilities: It created itself It came from nothing It has always been here i.e. it is eternal It was created If the universe created itself it would need to exist in order to do so, and if it's not there it can't create itself, so it is not reasonable to claim that the universe created itself. Next, the universe came from nothing. However, we never see things pop into existence out of nothing; it's not how our world and universe work so it is an irrational claim and we can cross that off the list. As for the third possibility that the universe has always been here is also irrational because we know that the universe is limited as it is made of limited celestial bodies (each body has a beginning eg. the planet earth and an end eg. stars that burn out) so it couldn't have always been there for millennials. Hence the universe is not eternal. The last option - it was created - is the only rational explanation of the origin of the universe. The universe shows numerous examples of intelligent design that point to the existence of a creator. All laws and patterns known in the fields of science and math have been created by a creator as well as those that have yet to be discovered. So where did the creator come from?  There are only 4 possibilities: He was created He appeared out of nothing He created himself He is eternal First, if you assume he was created, then whoever created him must be the real creator, and not him. So let's consider the origins of this creator and once again if we assume he was created we find we have an endless chain and we arrive don't arrive at an answer that makes sense. Next he appeared out of nothing. He just popped into existence - like magic. Well, nothing just appears out of nothing. We have already established that is neither reasonable nor rational. When you walk down the street do you see a phone-box pop out of nowhere or do you see people pop into existence out of nowhere and live in a house that just popped out of nowhere? No, you do not, so its not rational to think that the creator popped into existence from nothing. Now you may be looking at the third possibility and thinking it's silly, but it's a possibility. So have you seen anything create itself? Well let's take a look at, a table for example; it has a maker even though you haven't seen him. You know someone made the table, and it didn't make itself - common sense tells you that much. And to make yourself you need to be there in order to do it. So the creator didn't create himself. And that leaves the last one he is eternal. He has always been there. This seems the most rational conclusion of all four possibilities. The creator created everything, including human beings. Everything he created is limited but he himself is unlimited i.e. nothing like his creation and not a part of it. Because you were in fact created at one specific second, at a specific minute, of a specific day, so you know absolutely nothing that came before that second you were created. So, your mind has a basic idea of the world around you; everything has a beginning, like I have a beginning, and that is the concept that all creatures carry. Because they were created, they have difficulty imagining and visualising a being that doesn't have a "beginning" or an "end". In fact we interpret our world by time - beginning and end. understand that  the creator of everything also created time. It only exists because he created the concept. Before he created it, the concept of "beginning" never existed. The idea of  a beginning to everything is something that only exists in your mind because you were created with a beginning, but that doesn't mean that the same concept can be applied to the creator, because before he created time; beginnings and endings did not exist! So then, you probably, after taking that idea in, wonder to yourself "How does he exist if not within time?" Simply, he would have to exist in a place, where time is not a thing. Our universe has a beginning because he created it, therefore he cannot be living in it as he would have been living in his own way before he created this universe. Another possible question you might ask yourself is "Then, what is the 'present' time to God." And, to that I say, remember, he does not experience time like you do. Time is something he created for you. You experience past, present, future. He does not. He is outside of time as you know it, because he created time. He is not limited to time the way that you know it, and feel it. He is something different to you, in a place different from where you live. Put simply, the creator does not abide by the same rules that he has placed on his creation.  Conclusion It is inevitable that a person who ponders deeply upon the matter will invariably reach the conclusion that a creator must exist as the existence of a creator provides the only rational response to the existence of man, life and the universe. And through the use of rational thinking one can come to the conclusion that the creator is eternal and beyond anything we could ever imagine.