Heraclitus (540-475? BC) lived in Ephesus, Asia Minor but often preferred to wander among the mountains eating only vegetables.
He noticed that fire or heat produced changes in matter and considered this as the pervasive element of the universe. Heraclitus also noticed that the seeming stability of reality was an illusion because everything in nature is always changing.
There is nothing permanent except change.
The only constant is change.
Change is the only constant.
Change alone is unchanging.
(From Lives of the Philosopher by Diogenes Laertius)
So, there was something underlying nature which was a constant. What was it? "He asserted that the world is governed by a firelike Logos, a divine force that produces the order and pattern discernible in the flux of nature. He believed that this force is similar to human reason and that his own thought partook of the divine Logos." (Encarta Encyclopedia/Logos)
Although Heraclitus considered Logos divine, it is not clear if the Logos present and working in the universe was also separate from it.
Plato (427-347 BC) was a citizen of Athens and a pupil of Socrates. The search for God begun by Socrates continued with Plato.
Plato conceived of God as that which is always the same in whom there is no becoming and who is the cause of everything created. He reasons that in God there must be an eternal pattern of the universe which becomes realized in time. He states that God is good because in him there cannot be jealousy of anything and that he desired that everything be good like Himself. He makes an interesting observation -- "But the father and maker of all the universe is past finding out; and even if we found him, to tell of him to all man would be impossible." (Grat Books, The Dialogues of Plato, Timaeus, Encyclopedia Britannica, Inc., 1952, p. 447) He seems to say that we cannot really know God as he is in himself.
He did not exclude other gods from his vision. He states the men of old considered themselves as offspring of the gods and that we must accept their tradition although they give no proof of it. However, other gods are creatures --"Gods, children of gods, who are my works, and of whom I am the artificer and father, my creations are indissoluble, if so I will." (Ibid., p.452)
For Plato, God does not create out of nothing, instead there exists a mysterious, invisible and formless reality which can receive the intelligible forms God creates. Space, the home of all created creatures is also an eternal reality which cannot be destroyed. So, Plato moves forward in the understanding of God and how God may have created the universe.
Aristotle (384-322 BC) was also a citizen of Athens and schooled in philosophy by Plato, but unlike Plato, Aristotle viewed all motion in the universe as eternal, therefore, the universe always existed. However, Aristotle saw that moving entities were at times at rest, so they were only potentially in motion. He reasoned that there must be a mover who is always actual or in act in whom there is no potential motion, the Unmoved Mover.
Than Aristotle considered the possibility of many unmoved movers. He "determines that there could be only one unmoved mover, not only because many unmoved movers are unnecessary, but because only one mover could produce continuous motion, in the sense of being an interconnected system of cause and effect."
Next, Aristotle probes into the nature of the unmoved mover movement. He realized the motion was for a purpose and states, "The final cause, this produces motion as being loved, but all other things move by being moved." (Physics XII, 9)
final question of Aristotle is, "What does God think about?"
Since God is a unified spiritual being he cannot think of something else,
or have one thought after another. "Evidently, he [God] thinks of what
is most divine and precious, and does not change; for change would be a change
for the worst, and this would already be movement." (Physics,
XII, 9) So, God thinks about himself.
"Aristotle's God was clearly not a divinity to be worshipped. Apart from serving as the ultimate source of motion, God, ignorant of the world's existence, could play no meaningful role in Aristotle's natural philosophy. Nevertheless, Aristotle seems to have had a strong sense of the divine, which manifested itself in a sense of wonderment and reverence for the universe." (Web: Encyclopedia of Science and Religion/Aristotle)