Vishnu is the Purusha from which Indra and everything else originated.
Purusha is the origin of everything
The moon was born from his mind; the sun was born from his eye; Indra and Agni were born from his mouth, Vayu from his breath.”
- Rigveda 10.90.13.
Purusha is none other than Sri Narayana
The Purusha described above gave up the object which was beyond the scope of name and form, hard for worldly people to understand and took a form with a thousand parts and capable of giving Moksha on sight, for uplifting the suffering Devas and others. In that form, pervading the world he was beyond it by an infinite distance. This Narayana was the Past, Present and the Future. And was the giver of Moksha to all. He is greater than the greatest - none is greater than He. He made himself into four parts and with three of them exists in the heaven. By the fourth, the Aniruddha (for of) Narayana, all worlds have come to be. This (part of) Narayana created Prakriti (Matter) for making the worlds (Prakriti stands for the four¬ faced Brahma). In full form the latter did not know the work of creation - this Aniruddha-Narayana told him.
- Mudgala Upanishad of Rigveda.