The original worship of Vishnu, by the Aryan conquerors of India or the original Dravidian inhabitants is not definitely known. In the ancient Vedas, the body of literature known as the Veda, and sacred literature of the Aryan conquerors, Vishnu is ranked among the lesser gods and is usually associated with the major Vedic god Indra who in the epics and Puranas fights against dragons and demonic forces. These latter writings emerge during the later development of Hinduism.
It is throughout this literature and especially through incarnations that Vishnu is raised to higher rankings within the Hindu pantheon. He becomes the prominent second god of the Trimurti, the Hindu Triad, while Brahma is first and Shiva is third.
In some Puranic literature Vishnu is said to be eternal, an all-pervading spirit, and associated with the primeval waters that are believed to have been omnipresent before the creation of the universe.
The concept of Vishnu being the preserver of the world came relatively late in Hinduism. Presumedly it sprang from two other beliefs: that men attain salvation by faithfully following predetermined paths of duty, and that powers of good and evil (gods and demons) are in contention for domination over the world. When these powers are upset Vishnu, it is further believed, descends to earth, or his avatar, to equalized the powers. Further it is thought that ten such incarnations or reincarnations of Vishnu will occur. Nine descents are said to have already occurred, the tenth is yet to come. Rama and Krishna were the seventh and eighth.
Another interesting speculation concerning Vishnu's role as preserver among many modern scholars is that it is characteristic of the practitioners of Hinduism to raise local legendary heroes to gods in the Hindu pantheon.
Vishnu is portrayed as blue or black shinned and has four arms. He has a thousand names and their repetition is an act of devotion.