I'm not sure why this topic is in the Atheist forum and not the Christian forum, but I guess that it doesn't much matter.

Perhaps one way to get at the question is to go all the way back to Aristotle, who argued for a 'first cause,' an 'unmovable mover,' etc.  The argument is derived from making inferences from experience to the proposition that at the very bottom, the final regress, is something that is qualitatively different than that which follows.  Thus, even without knowing anything else about the nature of this final regression, it can be said that it differs from the rest of reality in that it itself requires no causation, ie, it is non-contingent.  Aquinas takes this argument and adapts it, but suffice to say for this thread that the entity defended is, by definition, non-contingent.  Insofar as anything is contingent, it is not in the same category of things under consideration as 'God.'

Contingency is a tricky concept, but I think that most polytheistic religions have some way of acknowledging a non-contingent god that takes precedence over all the rest.  In the case of Christianity, there are also lesser spiritual beings that are not called contingent gods, but often play the role of a contingent pantheon.  Protestantism seems to place less emphasis on such beings than Catholicism does.  For atheists, of course, there is no non-contingent intelligent agency, but physical reality itself can be considered non-contingent.

Thus, by way of contrast, Zeus, according to the mythology, emerged from the union of Cronus and Rhea.   Where did Cronus and Rhea came from?  They are not non-contingent, either, so still not in the category of entities postulated by Christians.  The same can be said about virtually every other entity described in various pantheons.  In contrast, to find examples of entities where the entity in question is non-contingent, we may turn to Brahama, in some brands of Hinduism.

Although I have seen the spelling 'Brahama', my guess is that that is a corruption of the pronunciation based on the way it is spelled in Hindi.  There is no vowel following the 'h' in Sanskrit, and that is made clear in some forms of devanagari script.  The god's name is better represented as 'Brahma' or 'Braahma'.  Brahma is part of the so-called Hindu trinity, or 'trimurti'--Brahma, Vishnu, Shiva--which, like the Christian trinity, represents three aspects of the same being.  Do not confuse Brahma with Brahmanas (or Brahmanah or Brahman), which is something like the 'oversoul' of the universe.  It does not refer to a personal god in the Christian sense.  The creator god, Brahma, does, and there is a god called Ishvar that may refer to a personal manifestation of Brahmanas. (There are so many different takes on Hinduism that it is hard to make definitive statements about how all Hindus view their gods, but the same can be said of Christianity.) As for contingency, I don't really know how most Hindus would approach Brahma.  My guess is that Brahmanas or Ishvar would be considered the non-contingent component in their religion.  (Actually, this is what one Hindu once told me in trying to expalin the difference between Brahma from Brahmanas.)

Greeks and Romans, too, had a concept of non-contingency.  After all, Aristotle was not a Christian, and his works only survived because the Arabs preserved them.  However, their concept of the 'Demiurge' is sometimes described as the noncontingent god that created all the others.  (Gnostics had a different concept of demiurge, from what I've read.)

But this raises another difference between the Christian 'God' and various usages of the word 'god', because Brahama IS the universe in these schemes, so that the universe itself is non-contingent, but is also identified with personality.

Well, you may be confusing a trimurti aspect--Brahma--with Brahmanas here.  It is Brahmanas that is identified with Atman or 'oversoul'.  However, Westerners often confuse the two, or so I'm told.  So your interpretation will be supported by a lot of descriptions of Brahma out there. 

The Christian God is not identifiable with the universe on a one to one basis in this sense, because the entity meant by the Christian 'God' is asserted to trancend the universe.   The universe is not an expression of God's 'personality,' but rather a potential medium for the expression of that personality.

Hmm.  I'm not sure what difference all of this makes in the end.  Is there a point to making this distinction?  I think that I understand your concept of immanence, which the Christian god with the Hindu Brahmanas concept share.  The Christian is very much like Brahma in the sense that God is a 'personal' god.  That is, humans accord him social status and can have a personal relationship with him.  That would also be true of the contingent Hindu gods, but not the 'oversoul', atman, or brahmanas.  Brahmanas is supposed to be inconceivable and transcendent, which are also considered attributes of the Christian god.  I agree with you that the personal god of Christians is not quite the same as any of the Hindu gods.  However, non-contingency is definitely a part of their spiritual world view.

However, if there is only one non-contingent reality, everything else is contingent on that reality, meaning that while Christians maintain that God trancends the universe, it must be the case that the universe cannot exist at all apart from the energy and working and sustaining of God, out of his own essence.  The word for this is 'immanence.'   Deism is pure transcendence.  Hinduism is pure immanence.  Christianity is both/and.  An entity described as such is detectable only across a narrow range of KINDS of evidence, most of them requiring revelation from God down.  If we are bound within the system, and our senses are restricted to the system, but the entity stated to exist exists beyond the system, then it follows that the only reliable information about that entity (other than perhaps the inference it exists) will come via revelation.  This entity must come in;  we cannot go out.

OK.  I think that we have rough agreement.  The various religions have different ways of dealing with the non-contingency issue.  Deists view God as disinterested and irrelevant to human concerns.  The Hindus and other Indian religions are all over the map on these issues.  There is still a generic concept of a god as a spiritual being that humans can relate to on a personal level, however.  The Christian God just doesn't separate out some of the attributes that other religions do.

This is qualitatively different than many, if not most, if not all, other entities casually and sloppily termed 'gods,' who usually can be considered to be much the same as superheroes in the Justice League.

I certainly don't agree with this assessment.  There is a sense in which Christians do treat their god as a superhero.  What is Jesus, if not that?  ("Jesus Christ, Superstar, who are you..?"  "What if God were just one of us...?")  God also has other properties.  The best case that you can make here is that the Christian God is a unique blend of properties that doesn't quite match up to the gods in other religions.  But Yahweh himself had to recognize other gods in order to put in his covenant that his worshippers not worship the other ones, as well.  So there is a sense in which even your own god blesses the "sloppy" linguistic usage that you decry here. 

Sntjohnny, it would have helped me to understand your point if you had explained the relationship of that passage to what I said.  My reaction to C.S. Lewis on this subject is that he makes egregious oversimplifications with dismissive statements of that kind.  Buddhism was no more a "simplification" of Hinduism than atheism is.  It grew out of an ascetic tradition that also spawned Jainism.  Nor was Islam really a "simplification" of Christianity.  But C.S. Lewis himself was a fairly unstinting supporter of British imperialism, and his Narnia classics are often criticized for their pro-colonial attitude.  Like many imperialists, he tended to look down on conquered peoples as uncivilized and simplistic.