"yada yada hi dharmasya, glanir bhavati bharata, abhyutthanam adharmasya, tadatmanam srjamy aham"

The Lord has saved the Vedas in His form as a fish, and He has borne the whole universe on His back in the form of a tortoise. He has picked up this earthly planet from the water in the form of a boar. He has killed Hiranyakasipu in the form of Nrsimha. He has cheated Maharaja Bali in the form of Vamana. He has annihilated all the dynasties of the ksatriyas in the form of Parasurama. He has killed all the demons in the form of Lord Rama. He has accepted the great plow in the form of Balarama. He has annihilated all the atheistic persons in the form of Kalki. And He has saved all the poor animals in the form of Lord Buddha. From Srimad-Bhagavatam it is understood that as no none can count how many waves there are in the ocean, no one can count how many incarnations are coming from the Lord's body.

In the Puranic mythologies of ancient India, the legend of the Avatar is considered one of the most important myths of the Vedic culture. It is particularly associated with the God Vishnu, one of the principle deities of the Hindu trinity which also includes Brahma, the creator and Shiva, the destroyer.
Vishnu is the preservation aspect of the trinity and represents that all-pervading power which maintains the universe and the cosmic order. He is considered to be the embodiment of goodness and mercy and periodically intervenes in terrestrial evolution by descending to earth in a human incarnation as the Avatar. The primary role of the Avatar is to re-establish stability and order on the earth and to introduce a new evolutionary impulse which will uplift mankind into a greater and more unified consciousness.

Because their periodic manifestation is determined by an inherent association with the Time Spirit, they take birth at particular points in the cosmic cycle which correspond to the earth's passage through the zodiacal ages.

In the Bagavad Gita, one of India's most sacred scriptures the 8th Avatar Krishna reveals himself to his disciple, Arjuna and discloses something of this cosmic process, "Whenever the world declineth in virtue and righteousness; and vice and injustice mount the throne, then cometh I, the Lord and revisit my world in visible form, and mingleth as a man with men, and by my influence and teachings do I destroy the evil and injustice and reestablish virtue and righteousness. Many times have I thus appeared, and many times hereafter shall I come again?"