Assuming the universe started somewhere, I'd put it down to some form of force, as much a deity as gravity is. I suppose I should edit my definition - a god is a creator ex nihilo which has sentience.
No, sentience is not really necessary.
(admission: Hard agnostic mode ON)
From what I have seen/read about Christian god, and various other gods in other pantheons, a god need not be sentient, awake, or active. Passive gods exist in several pantheons.
Take for instance, the role of the DF.EXE process in world creation in dwarf fortress. It runs "extra dimensionally" to the world(s) it generates and manages. It knows everything. Oversees everything. Everything obeys the order it demands, and deems everything that obeys its ordered mechanical rules as being good. (When working correctly anyway) The process is the actual "god" to dwarf fortress worlds. The player represents an input to that god. The process is static. It does not change itself on disk unless you update to a new version. It creates worlds ex nihilo.
It is not sentient.
Similar arguments could be made (in a vacuum anyway) about Old Testament god. Old Testament god exists prior to the creation of the universe. (Exists extradimensionally to our universe, by necessity.) Old Testament god asserts that he is inside all of creation. (The same is true of DF.EXE, with DF worlds. Everything (in the game) exists inside the process's allocated memory footprint. Thus, everything in the game represents a part of that process-- the statement is literally true.) OT god is static and unchanging (like the DF process), and "Timeless"; The beginning and the end. (As is the DF process to DF worlds.) OT god is omniscient and omnipotent (As is the DF process to DF worlds.) but seems to be either unwilling or unable to disclose itself to its creations. (The DF process does not go out of its way to tell Urist that yes, he is running inside a simulation, and here's how to manipulate his own simulation logic either.)
The typical arguments against omniscient and omnipotent gods usually boils down to an implied fallacy-- That these beings need to adhere to a creed about "benevolence" that caters to human pleasure centers. This implication is not a requirement. Instead, the goal appears more to be self-consistency, with self-affirmation and consistency of the systems they manifest as being the primary objective "Good" these entities strive for. The benevolence of these beings is that they create and maintain systems that enable humans and human thoughts. (Much like DF enables dwarven thoughts. It is not that DF.EXE needs to always assure that Urist is bathed in alcohol, and that goblins never invade-- Even though the game engine is quite capable of doing this. INVADERS=FALSE does nearly all of that in the config section. Does the game do that by default? No- What is considered "Proper behavior" by the game is for Urist to have his brains splattered across several tiles when the trolls come and bash down the door, and smash his head in with a giant club.) OT god seems to have created the universe to reaffirm his own views about how an orderly creation should be operated and maintained. The creation of humans is to reaffirm the authority and integrity of the OT god-- Not to bathe humans in pleasure up to their eyeballs.
With that in mind, other arguments against the omnipotence angle become tautologies. "A god that is capable of anything is capable of self destructing!" etc. Yes. and DF.EXE is capable of initiating self-termination. That does not mean that self-termination is a good thing, or is the intent of the omnipotent god. Termination of the simulation is against the ethos of the creator-- which creates the simulation, to have a simulation. Self termination destroys the simulation. The god is capable of this, but does not wish it/does not consider it a very useful thing to do. Pretty much all arguments in this intellectual bent hit this block when viewed this way.
The more I have contemplated the possible modes of existence of an actual divine creator, the more I have come to favor the idea of a completely non-sentient process, such as this. It makes decisions, but is not sentient. It operates entirely on its own internal order and mechanics, and is not "willful". It all at once explains the seemingly capricious nature such a divine creator must have (Really, as long as the laws of physics are obeyed, anything goes-- and why seemingly contrary things are considered "good") as well as why the creator appears indistinguishable from a simple force of nature. Philosophical question: Is DF.EXE "natural", or "artificial"? To the simulated dwarves living inside its process, would it not just appear to be nature itself?
Granted, this is a completely different kind of theism to the human-like gods of nearly all religious pantheons. It however, is a valid interpretation of a divine creator god. It has similarities to the "Sleeping god creates universe by dreaming" archetype, but being non-sentient, is not actually dreaming. The existence of the universe is instead the result of the active machination of this god, which does what it does for its own reasons, completely divorced from what the child processes inhabiting its simulation want or feel.
After a rather long time cogitating this, this appears to fit the "holy spirit" incarnation of the OT god perfectly. Pretty much any descriptive verse of this entity can be explained through this mechanic. The existence of the "divine savior", the christ, can be explained as an error correction routine being spawned to herd misbehaving subprocesses back into line, rather than simply terminating them.
"Machine god" is a perfectly valid kind of god. The fact that you cannot sway the machinations of machine god with politics is inconsequential. That machine god does not have actual desires or wants, is also inconsequential. The fact that worshiping machine god does not change machine god's mind is inconsequential. Machine god has already decided everything, and does not need to change its mind.
I cannot discount the existence of such a wholly self-consistent, deterministic, mechanical 'god' being behind our universe's physics. To us, its active machinations would be indistinguishable from fundamental forces of nature. The parameters it has set for the simulation simply are. (Why does an electron have the spin and charge that it does? et. al.) From machine god's POV, our debate about machine god is moot-- We obey its rules, regardless, and that is good. If you choose not to believe machine god is a god-- machine god does not care. If you choose to believe that machine god is a god, machine god does not care. It is only when you try to break physics, that machine god cares. The closest thing to direct imaging of machine god in action is going to be things like spontaneous symmetry breaking, and the fact that at the deepest level, our universe exists in a quantized fashion, with discrete quanta of energy. (when you try to say, go smaller than the plank length, you see machine god's hand slapping you, saying "no, plank length is the smallest allowed length.")---Everything else derives from the simulation maintained by machine god, and machine god thinks this is good.
I cannot prove that machine god is "a god." That appellation is moot. The universe exists, and is quantized in nature. That is all that I really need to know or care about.