An avatar (अवतार) is a concept in Hinduism and it means "descent". It refers to the appearance or incarnation of a deity. Initially, it was used to refer to any revered guru or human being in post-Vedic literature. Some stories, refer to persons who are endowed with a mysterious power of assuming any form. Though Vishnu avataras are popular, there are avatar stories for sakthi, devi and other deities. Incarnation concepts similar to avatar are also found in many countries.
The Avatara doctrine is about divine descent of Vishnu into the world for the establishment of Dharma and protection of devotees. Number of avataras vary, from 10 to 22. Dasa avatara is still a popular concept. There is no reference of Avatara in the Vedas, but elaborated in the Puranas and Epics.
Divine Fish saving people during great floods is very popular in all cultures. As a fish (matsya), Vishnu saved Vaivasvata Manu from the flood that enveloped the world. The matsya motif also represent the rise of new constellation at the plane where the celestial equator intersects the ecliptic. The old constellation goes below the plane (the old earth sinking) and the new constellation rises up. Also age of pisces (fish) zodiac sign, have many legends. The plane of the celestial equator is metaphorically alluded to as the "Earth" in the old language of myth that we now do not fully appreciate. This change of the constellations occurs due to precession of the earth's axis as it spins.
The kurma/ samudra manthana is also connected with this precession of the axis. The churning of the ocean with the mandhAra rod (axis) is a direct pictorial representation of the axial precession.
Varaha lifting land mass is developed from stories on land reclaimed after psunami. Kurma and Varaha, may be based on land movement due to major earthquakes and tsunamis. Around 1600 BCE, a tsunami caused by the eruption of Santorini destroyed Minoan civilization on Crete and related cultures. Curvature of earth, makes land mass look like tortoise shell. After tsunami (evil asura who pushed land mass in to seas), in form of a boar, Vishnu rescued the land mass from the oceans or underworld. There are many ancient scientific texts on seismic and volcanic activity.
Vishnu became narasimha, a being who was half-man and half-lion. He killed the evil asura Hiranyakashipu as narasimha. There are tales of a child saved from an evil person by lion. There is a folk tale, in which an evil leader challenges if God is every where. When he hits a pillar, due to force roof falls and he is killed by Yali (half lion/elephant) statue. Varahamira story refers to princes killed by metallic boar emblem.
In the form of dwarf (vamana), Vishnu was to hoodwink the asura Bali and restore the gods to heaven. Maha Bali, with the help of Shukracharya, conducted Yagna. Yagna may mean Research. Bali had taken an oath to award and support scholars with their wishes. Vamana turned up at the Research site in the shape of a dwarf. Bali was won by Vamana, by his intelligent requests or questions."
Minor incarnation as two sages named Nara and Narayana.
Kapila taught samkhya yoga.
Dattatreya an avadudha, the son of Atri and Anasuya.
Vishnu was born as Urukrama, the son of Nabhi and Meru. He taught everyone the righteous way of life.
Vishnu became the king Prithu and restored foodgrains and herbs to the earth.
Dhanvantari, physician of the gods and the originator of medicine.
In mohini avatara, Vishnu adopted the body of a beautiful woman so as to charm and rob the asuras of the amrita (a life-giving drink).
Vishnu became Parashurama, killed all the kshatriyas in the world twenty-one times. Kartavirya abducted the divine wish-fulfilling cow (kamadhenu) and her calf from Sage Jamadagni’s ashram. This incident occurred in Parshuram’s absence. On His return, realising what had happened, He vowed to slay Kartavirya. In the ensuing battle between the two on the banks of the river Narmada, Parshuram slew Kartavirya. Thereafter complying with His father’s directives He embarked on a pilgrimage and to undertake austerities.
Vedavyasa, the son of Parashara and Satyavati.
Incarnation was as the sage Narada.
Rama as role model for the world.
Vishnu became Krishna.
Last incarnation is yet to come Vishnu will be come. Vishnu will be born as Kalki so as to destroy evil in the world and restore righteousness.
Some texts include many great personalities like Buddha, as avatars.