Between the Vedic and Epic periods, the divinity known as Vishnu underwent a cosmic change. In the Vedas, Vishnu was a minor solar god who was closely associated with Indra, in which he was rarely mentioned and was submissive to the king of the gods. By the time of the epics of the Mahabharata and the Ramayana, Vishnu had greatly risen in importance and power in the world of the gods. Vishnu is now known as "The Preserver" among the three books of the Hindu religion. Vaishnavas, worshippers of Vishnu, made up 70% of Hindus in 1997. (Dom, Chapter 2) Based off Vishnu Purana and the Vaishnavas, Vishnu plays the role of Brahma and Shiva as well in which he creates himself, preserves himself, and then at the end of each cosmic cycle, destroys himself. As Brahma sits in Vishnu's navel and Shiva is a recluse in the mountains, associated with death and destruction, Vishnu is given the importance of an omnipotent, omnipresent, and omniscient, supreme divinity. There are several different theories on what lead to this revolution of power among the Gods. Some scholars believe that Vishnu's rise was inevitable because of his close association with the concept of Vaikuntha (heaven). (Gonda, p.2) He dwelled in the realm in which many sought to reach by showing their devotion. Another theory is that in the Vedas, Vishnu was personified as sacrifice, and therefore was the first one to comprehend its true significance. According to a particular myth, many gods were jealous of Vishnu's rising power and had him decapitated. His sacrificed head then became the sun. Finally, there is speculation that Vishnu is an incorporation of three important Vedic gods. He was a fusion of his original being Vishnu: the Vedic sun god, Narayana: the cosmic deity, and the man-god Vasudeva-Krishna. (Gupta pp. 1-3) Vishnu had tremendous popularity which was because of his connection with the people. Vishnu came to earth in human or animal form through his incarnations to directly aid his devotees and save them from imminent danger. The incarnations follow a cosmological cycle, in which one appears in each phase. Vishnu appears on earth in order protect dharma and restore order to the world. In the Bhagavad Gita, Krishna, the eighth avatar of Vishnu explains to Arjuna, "Whenever righteousness declines and unrighteousness prevails, I manifest Myself; For the protection of the good, for the destruction of the wicked and for the establishment of righteousness, I am born in every age." (Bhagavad Gita, IV.8) (Krishna pg. 30) An alternative explanation for Vishnu appearing on earth may be due to a story from the Vedic period. During a battle with the asuras, the mother of a priest named Shukra was able to use magical powers and leave Indra, the king of all gods, impotent. At Indra's bidding, Vishnu reluctantly cuts off her head, killing her even though she was a woman. Shukra, who was outraged, cursed Vishnu to be born seven times in the world of men which include Parashurama, Ramachandra, Buddha, Kalki, and several minor incarnations. (Gupta pp 9-10)
There have been nine main incarnations of Vishnu, and one is yet to come. Although the Bhagavata Purana mentions twenty-two avatars, and the Ahirbudyhnya Samhita mentions thirty-nine, the most commonly accepted number is ten, from the Varaha Purana. The first three incarnations are animals, and were at once considered manifestations of Brahma. Over time, these stories, like many others, were accredited to Vishnu. The ten forms he takes on earth are all related in their common images and symbolism, there are also patterns to be seen as each incarnation appears. Each of the avatars has certain attributes of the all pervading Vishnu. From studying some of the symbolism and characteristics of each avatar, we can see the reason behind Vishnu's popularity, his connection with Hindu principles, and how he has come to be known as the benevolent divine being.