It was a period when the earth was under the ruling of monarchs across the globe, everyone eager to expand their domains further and further. As a result, arose powerful civilizations filled with the richness of languages, architecture, technologies, medicines and more. But this was not all, surprisingly every civilization/city/town had a dedicated god or goddess, and the monarchs used to give the credit of his victory in battle over his rivals or the technological and economical feats that he accomplished to the dedicated deities by constructing megalithic structures or portraying the deities statues in city halls. It is believed that ancient kings used to please and appeal those deities who descended from the skies, so that there was economic prosperity in the kingdom, and used to have an upper hand in battling his rivals. These are some of the ancient civilizations and their primary deities :
  • Ancient Mesopotamia = Anu/Enki
  • Egyptian civilization = Amun
  • Ancient Greece = Zeus
  • Indus valley civilization = Rudra
while most of the ancient scriptures depict how ancient kings held victorious with the backing of gods, there is a scripture that stands apart, that explains how to please the gods and get a favor from them, with detailed hymns and explanation, they are collectively called Vedas, a Sanskrit word for knowledge, the book of Veda's is sometimes also called as apauruṣeya, which means "not of a man, superhuman" and "impersonal, authorless", some times as śruti “what is heard" it is believed that Lord Brahma (the creator of the universe) dictated the Vedas to the ancient sages, the knowledge of Vedas was scattered and unorganized before the sage Vyasa divided the Vedas into four parts as:

All of these texts are written in an ancient language of Sanskrit, the language which is considered to be the language spoken by the gods themselves. And the texts also have a clear distinction between God who is also called as Ishvara or Brahman, (who is beyond birth and death, who is the creator and the destroyer of the universes,) and the deities to whom the hymns in these books are dedicated to are considered to be the higher dimensional beings who are in charge of the universe but are considered to be mortals but with a longer lifespan than we humans in the spacetime, due to the effect of time dilation as per the books of Puranas.
While the hymns of Vedas often mention the god who is the creator of humans as well as the deities to whom the Vedas are dedicated to, most of the Vedic hymns are dedicated to the lord of the  Deva's the Indra/Zeus/Ashur who is also the lord of the universe (de facto), followed by Agni(fire), the fire is considered to be the portal between humans and gods through which humans can please devas to get the boon, and followed by other deities which include few celestial messengers and scholars of them.
Lord Indra/Zeus offering nectar of immortality, mount Meru in the background, guarded by Angels.
The kings of ancient times did please these deities through fire sacrifice, animal sacrifice and many more with personal and social interests such as technological aids, economic aids, while few kings who felt the inferiority of being humans did plead them to change his human form to another, the technologies that I have mentioned in my previous article. MYSTERIOUS TECHNOLOGIES OF ANCIENT GODS!
The truth of Vedic deities who were considered to be the gods in the past is clarified in the book of Bhagavad_Gita in verse  9.25:

"Worshippers of the celestial gods take birth amongst the celestial gods, worshippers of the ancestors go to the ancestors, worshippers of ghosts take birth amongst such beings, and My devotees come to Me alone."
Apart from Vedas, there were a lot of incidents recorded and mentioning of extraterrestrial origins of those deities, their arrival their influence on humans in ancient times and their departure in books such as Mahabharata and Purana's. 
Alongside the extraterrestrial race of devas, there were a lot of other races mentioned in different Hindu scriptures such as  Asura Daitya Rakshasa Gandharva Danava Kinnara who were mentioned as extraterrestrial origins and fought with each other to hold supremacy over planet earth.