God. (Yes, the Big Question!)
I 'm a Christian in the sense that align myself with a particular group of people; I try to follow the pattern of Christ; and I support the intentions of those who assert the words of the Creed: "We believe in God, the Father almighty, maker of heaven and earth, of all that is, seen and unseen.... etc." Note the 'We' in this, rather than "I", a thoughtfully change made some 30 (?) years ago so as to accommodate people like me! The crunch of this is, what/who is God?
I'll start with Douglas Adams' famous comment in "The Hitchhiker's Guide to the Galaxy":
    “Space is big. You just won't believe how vastly, hugely, mind-mindbogglingly big space it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

He's right. Indeed I want to go even further. What we call "space" is  a conception of human beings - creatures on a small planer who have evolved a capacity represent in words the nature of everything they encounter. Space (or what I, when a physicist, would have called "space-time", because you can't separate space and time at this vast level)  is the connected continuum within we and everything that we know is contained. 
 To go beyond Douglas Adams, can we talk about the entirety of all all that is, whether we understand it or or whether it has no connection at all with the comic universe and is totally inscrutable?
Yes, but it doesn't mean anything? The writers of the Creed probably would propose that God could create this also.