Vishnu is one of the three main gods of the Hindu trimurti (three forms). The trimurti is often depicted in art as one man with three heads. Brahma is the Creator. Vishnu is the Preserver. Shiva is the Destroyer.
The name Vishnu comes from the Sanskrit root 'vish', meaning to pervade. Some Hindu legends describe Vishnu as an eternal deity, and associate him with the primeval waters that pervaded the world before creation. Another name for Vishnu is Narayana, meaning 'one who moves waters'.
To understand Vishnu's role as Preserver, one must accept two basic Hindu beliefs. The first is that humans may escape the cycle of samsara by following predetermined paths of duty. The second is that good and evil are in constant contention for their reign over the world.
It is believed that whenever evil outweighs good with an opportunity to emerge victorious, Vishnu descends to earth in some mortal form to save humanity. Vishnu is not allowed to tamper with events directly. Rather, he intervenes and guides humans to act in ways that will restore proper balance between good and evil.
The puranas speak of the ten avataars of Vishnu. These incarnations detail the divine help given by Vishnu during various stages of human evolution, by appearing on earth in different forms. These avatars are said to demonstrate that divinity re-establishes Dharma or righteousness and destroys injustice from time to time, by appearing on earth in various incarnations.
The ten avataras are Matsyavatara (fish), Koorma (tortoise), Varaaha (boar), Narasimha (the man lion), Vaamana (the dwarf), Parasurama (the angry man), Rama (the perfect human), Balarama and Krishna (the divine statesman). The 10th avatar which is yet to appear is Kalki.
Matsyavatara, or the form of the fish was taken up by Vishnu during a deluge that submerged the earth. Vishnu commanded a rishi to gather together samples of all species and wait in a boat. The gigantic golden fish then dragged the boat through the deluge and then enabled Bhrama to start the act of creation all over again. Yet another legend has it that a demon once stole the four Vedas and hid them under the sea. Vishnu assumed the Matsya form and retrieved them and then restored them to their original fragrance. This legend is held at the Parimalaranganathar temple at Mayiladuturai, near Thanjavur (Tamilnadu).
The Koorma Avatara where Vishnu took the form of a tortoise, is described in the legend of the celestial nectar Amrita.
Vishnu took the form of a wild boar - the Varaaha Avatara, dived into the ocean, and saved Bhoomi Devi who sank into the bottom of the ocean, with his massive snout. Vishnu as Varahamurthy is enshrined at Tiruvidandai near Chennai, and at the Kanchipuram Kamakshiamman temple.
In his Narasimhaavataaram, Vishnu destroyed the demon king Hiranyakashipu and demonstrated his omnipresence in a powerful way.
Vishnu took the form of Vamana the midget to destroy the demon Bali. He visited Bali during a sacrifice where the latter was arrogantly distributing gifts of the seeker's choice, to show his power of wealth. Vamana meekly asked for three feet of land measured by his small feet. All on a sudden he assumed the massive form of Trivikrama, dominating the universe; with his first foot he covered the earth, with the second the heavens. When there was no room for the third, Bali, who never went back on his word offered his head, and Vishnu sent him to the netherworld. Trivikrama is enshrined at Tirukkovilur, Kanchipuram and Sirkazhi in Tamilnadu.
Vishnu then took up the form of Parasurama, to quell the arrogance of the Kshatriya rulers who harmed the sages and unprotected mortals.
The Ramayana speaks of the glory of the Rama Avatar, and the Mahabharata speaks of Balarama and Krishna.
Some schools of thought believe that Krishna was the eighth incarnation of Vishnu and the ninth was Buddha and that Vishnu took up the avataar of Buddha to purify Hinduism of excessive ritualism. He preached detachment, and the middle path consisting of eight fold virtues of right views, right resolve, right speech, right conduct, right livelihood, right effort, right mindfullness and right meditation.
It is believed that at the end of the current epoch, there will be a deluge when Kalki - the tenth and the last avatara of Vishnu, will ride forth on a horse to redeem humankind and re-establish righteousness.
There is a legend for each one of Vishnu's first nine avatars and how each one intervened to preserve the universally required balance of good and evil. Vishnu's tenth avatar, Kalki, the horseman, has not yet descended to earth. It is believed that his arrival will mark the end of this present age of evil, known as the Kali Yuga.
Vishnu often appears dressed in yellow robes, hence his name Pitambara, or the yellow-vested one. Although his traditional vehicle is a giant mythical bird called Garuda, Vishnu may also be depicted amid the cosmic waters, reclining on the back of the coiled serpent named Sesha.
If Vishnu is depicted as reclining on the back of Sesha, this is a sign that order is prevailing in the cosmos, and a proper balance between good and evil is being maintained throughout the universe. If Vishnu is depicted as riding or standing near Garuda, this is a sign that he is ready to descend to earth and interact with mortals to preserve cosmic order.
Vishnu's wife is Lakshmi, goddess of fortune, wealth, and prosperity. She is often depicted together with Vishnu, seated on Garuda.
Vishnu is a popular deity and is worshipped widely throughout India. He has 1,000 names, and devotees who engage in his name recitation and repetition are believed to accumulate great blessings.