I have heard of the Greek god, Chaos (the manifestation of the void), and of the Greek god Aither, (the manifestation of the upper air that gods breathe most often), but I can't find reference to any deities that personify 'space' or 'the cosmos.'
Who is the Western god(s) of Space and The Cosmos, if there is any?
For Egyptian, you'd have several choices. Going from the largest (at least in the Heliopolitian cosmology):
Nuun (Nun) is the cosmic ocean that our universe is a bubble in: https://henadology.wordpress.com/theology/netjeru/nun/
Atum includes the concept of "Completeness". In a sense He/She would be related to the universe we know, and precipitated himself/herself out of the Nuun.
Shu and Tefnut would be next- Shu having a complex set of associations including emptiness and light, and Tefnut with moisture (and another set of associations).
From those two came Geb- associated with Earth, and Nut with sky. The Nuun also passed underneath the Earth.
The above is a gross simplification, especially when you mix in all the other Egyptian creation stories.
Several of the Greek philosophers talked about a spherical Earth: they noticed that you could see stars in the Southern Egyptian sky that were invisible in Greece, the reverse being true for Northern stars in Greece.
This depends entirely on your stance of if you're asking for a sky god or if you'd prefer only "outer space", so to speak. Given that these are ancient cultures / mythologies we're discussing, it stands to point that perhaps they would have seen the two as synonymous, which was why historically the sky gods were said to be most powerful. For instance, some accounts that I've read in the past read that Zeus became King of the Gods only after he had drawn the lot for the sky, as opposed to either of his brothers (this can also be contested that he became King due to the fact that he was the one who overthrew his father and had to rescue his siblings, which is the most widely accepted version I've ever come across).
Going back the furthest you can in Greek mythology:
There will be Chaos, which was accepted as the "oblivion" or the unknown, and the first being to give birth to all others.
Some accounts tell of the Titan Queen Eurynome (commonly mistaken with Zeus' third bride, and some accounts have them as one and the same person who was an Oceanid).
And of course there is also Ouranos, who is well known as the father of Kronos and the rest of the Titans, and he was depicted as the night sky that hung over the earth, the lover and husband of Gaia.
Ouranos (Roman Uranus) is the Greek (night) sky god. You will find him at the beginning of Hesiod's Theogony. Wikipedia has an extensive list of sky gods, among whom you will find the Egyptian goddess Nut.
THe closest thing to a god of the cosmos in Norse myth would be Ymir, the first being. The ice of the cold realm of Nifhel and fire from the realm of Muspellheim met in the space between, Ginnungagap, to make Ymir. He was suckled by a cow, Audhumla. Another giant was born from between his feet, and a man and woman from his armpit. Later, the god Odin and his brothers killed him, and made the world from his dismembered body.
As Grimnismal says:
Out of Ymir's flesh | was fashioned the earth, And the ocean out of his blood; Of his bones the hills, | of his hair the trees, Of his skull the heavens high.
Mithgarth the gods | from his eyebrows made, And set for the sons of men; And out of his brain | the baleful clouds They made to move on high.
All this implies that there was something (and a cow) there before him, but it was in a pretty chaotic state. Unlike Nun, Atum, or Ouranos, Ymir literally is the cosmos.
I think the primordial Titan Oceanus qualifies.
The ocean might seem like an odd choice for a god of the cosmos, until you consider pre-classic era Greeks believed in a flat earth floating in an infinite ocean (personified by Oceanus). This infinite ocean was also where the heavenly bodies rose from and set into, according to Homer:
Homer, Iliad 5. 10 ff:
"The star of the waning summer [Seirios (Sirius) the Dog-Star] who beyond all stars rises bathed in Okeanos (the Ocean-Stream) to glitter with brilliance."Homer, Iliad 7. 422 ff:
"Now Helios of a new day struck on the ploughlands, rising out of the quiet water and the deep stream of Okeanos to climb the sky."Homer, Iliad 8. 485 ff:
"And now the shining light of the sun was dipped in the Okeanos trailing black night across the grain-giving land."Homer, Iliad 18. 43 ff:
"[Hephaistos depicts the cosmos on the shield of Akhilleus:] He made the earth upon it, and the sky, and the sea's water, and the tireless sun, and the moon waxing into her fullness, and on it all the constellations that festoon the heavens, the Pleiades and the Hyades and the strength of Orion and the Bear, whom men give also the name of the Wagon, who turns about in a fixed place and looks at Orion and she alone is never plunged in the wash of Okeanos."
The quotes are from here: http://www.theoi.com/Kosmos/Okeanos.html
Well the only ones I know of that you could count are all Greek:
One thing that must be pointed out is that all the Indo-European cultures (Germanic, Celtic, Slavic, Greek, Persian, Vedic...) are the same. They're simply different branches of the same culture/mythology, that originated due to regional separation, as the Indo-Europeans invaded/migrated to different lands and different populations settled in regions isolated from each other. Therefore the appearance of minor differences between these different branches is inevitable, but the main aspects are the same.
One of the first bigger historical civilizations created by the Indo-Europeans was the Vedic civilization in North India. In the Vedic cosmology, Brahma is the main God. He's everything, the universe itself, and the other gods are different manifestations of Brahma, avatars with different traits to be worshipped. The reason for that is the channeling of spiritual energy - in the Vedic texts, it's called Nirgunabrahman, the impersonal, attributeless Absolute, or Parabrahman, the Supreme Absolute.
The Celtic mythology is the one I'm most familiar with, so I can give you a more in depth example: Dagodeus is referred to as the vortex of existence, Trinertá. Dagodeus is depicted as a three faced God, that is the explanation for such a motif as a trinity being so present in Indo-European cultures. Other Indo-European deities such as Brigid are also three faced or have three manifestations/personalities. There are also Indo-European religious symbols such as the triskelion and the swastika that are a vortex always in movement. As you can read in a post in my blog I've written years ago:
...The universe emerged from a triad, Trinertá, the Three Forces. the three elements, ie, the two opposing forces and their resultant, arising from the first movement in the Immensity supra-causal and non-differentiated Bituimon. This triad is the primary basis for all aspects of the universe. These three basic forces are mentioned in cosmology as a centripetal attraction, a centrifugal force and balance.
The centripetal action, personified by Lugus, the immanent, the Preserver of the universe is called Biwotúts ("existence"), because there is a concentration of energy, a force of agglomeration. On the mental plane, the cohesive force is the tendency that lights up the unit.
The centrifugal action, called Demerá ("dark"), is the force that seeks to prevent the dispersion concentration. This tendency toward disintegration is the symbol of the final dissolution of all existence in Non-Being. It therefore represents a release. This force of annihilation is personified by dits firing, the Destroyer of Worlds, also called Dagodéwos, Good God.
The balance of centripetal and centrifugal gives rise to the third trend, the tendency to orbiting, Suimon, which is the source of the activity. She is personified by the Creator, He-Who-Is-Eternal Bitumios...
Myth-wise, the deities in these different cultures can vary, while there may be in one culture in a certain location a deity that personifies the universe, originally it's the main God that is the primordial energy of life (Brahma). In the Greek mythology that would be Zeus, in the Celtic mythology it would be Dagda (or Dagodeus in Gaulish), in the Persian Zoroastrian religion it would be Ahura Mazda, and in the Germanic mythology, Odin certainly. This primordial spirit is the essence of everything that is and ever was.
In Greek mythology, there is Asteria, the goddess of stars, and a few deities for the "moving stars". Helios was the god of the sun, and Selene was the goddess of the moon. Otherwise, Ouranos is the god of the heavens, meaning space too.
