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.