Abhyuttanam Adharmasya Tadaatmaanam Srujamyaham ''
'"Paritranaya Sadhunaam Vinaashaya ch Dushkritaam ,
Dharmasansthapanarthaya Sambhavami Yuge Yuge ''
Narrates Krishna to Arjuna : Whenever (Dharma, or the situation of law and order, is endangered on this world, I incarnate onto this world to re establish Dharma, law and order, and to protect the Sadhus or saints and to detroy the evil elements of the society. )
Avatars of Lord VISHNU.10http://sound-hindu-god-photo.blogspot.com/search/label/VISHNU
Lord Vishnu's preserving, protecting powers have been manifested to the world in a variety of forms, called Avatars, in which one or more of his divine attributes were embodied in the shape of a human being or an animal or a human-animal combined form, possessing great and sometimes supernatural .
Before the latest creation of the present universe, the four Vedas (the holy books delivered from the mouth of the Supreme-God) remained drowned in the waters. It was necessary to get hold of them to instruct Brahma about the work of creation. Vishnu was therefore appointed to bring up the Vedas from the deep. He took the form of a fish (matsya), descended into the waters and brought up these sacred books. 
Kurma AvatarLord Vishnu assumed the form of a tortoise and took the newly created earth on his back in order to render stability to the trembling globe. It is believed that even to this day the earth is supported on the back of this tortoise.
The Story of KURMA Avatar
In KURMA Avatar, Lord Vishnu incarnates himself as a turtle. It is an interesting story involving both the gods (devtas) and asuras (demons). In the ongoing saga of battle between the gods and asuras, on one occasion the gods suddenly lost all their strength due to a curse by the short-tempered sage Durvasa. The sage had once presented a garland of flowers to Indra, king of gods, who carelessly gave it away to his elephant which trampled it.The Devtas approached Vishnu for help. Vishnu then asked them to churn the ocean of milk after adding medicines into the ocean. Mt Mandara could be used a the churning stick he said. He requested them to ask them help of Asuras in lifting the mountain in exchange for offer of the share of nectar of immortality that would ensue from the churning. Both the devatas and the asuras churned the ocean using the serpent Vasuki as the rope. At the start, playing a Machiavellian trick, Indra, king of the gods asked the asuras for the head end of vasuki. But asuras suspecting foul play, took the head end, only to be deceived as the poison from Vasuki was slowly weakening them. But as churning was proceeding the mountain was sinking and then Lord Vishnu took the form of the turtle KURMA and kept the mountain afloat. As soon as the bowl of amrita, the nectar of immortality was out, the asuras grabbed it. Then Lord Vishnu took the form of an apsara, a beautiful maiden, and seduced the asuras into letting her distribute the nectar and also to abide by her order of distribution. As soon as the devatas were served the maiden disappeared thus totally deceiving the asuras and making them totally weak.
3-Varaha Avatar
(The first mammals evolve (60 million years ago)
In periodical destruction of the world, once the earth sunk into the deep waters. Lord Vishnu, the great preserver, taking the form of a boar (Varaha), descended into the waters and drew up the earth with the help of his tusks
In VARAHA Avatar, Lord Vishnu incarnates himself as a boar in this world. A demon Hiranyaksha, had prayed for Lord Brahma and got awarded a boon that no beast nor man nor god could kill him. But somehow from the list of beasts the name of boar was missing. This proved to be his lacunae. He then started a campaign of plunder across the worlds. He pushed the world to the Pataal loka, or the under of the sea. He stole the Vedas, the holy scriptures from the Lord Brahma, while he was asleep and performed huge atrocities. To retrieve the Vedas and to save the world the Lord Vishnu assumed the role of a boar and brought out the earth from the under of the ocean, using its two tusks. It then killed Hiranyaksha and retrieved the Vedas from the asura and brought it back to the safe custody of the Lord Brahma.
4-Narasingh Avatar
(half man-half lion)
Half man-half animal appear (30 million years ago)
The Story of NARASIMHA Avatar
In NARASIMHA Avatar, Lord Vishnu incarnates himself as a semi-man, semi-lion in this world. The king of demons (asuras), Hiranyakasyapa, wanted to become immortal and wanted to remain young forever. To this end, he meditated for Lord Brahma and because of his severe penance, the gods were frightened and asked Brahma to pacify the king. Brahma was impressed by his austerity and granted him a wish. HiranyaKasyapa wished that he be neither killed by a man or beast, nor in daylight or at night and neither inside or outside a building. Having obtained the wish he considered himself the supreme God and frobade all worship of gods by anyone. But his son Prahlada, was an ardent devotee of Vishnu. This enraged Hiranyakasyapa very much. He ordered numerous ways to kill Prahlada including asking his sister Holika to sit with Prahlada in the fire. But everytime Prahlada escaped unhurt. Enraged, once he asked Prahlad to show him the Lord Vishnu. Prahlad said, "He is everywhere". Further enraged, Hiranyakasyapa knocked down a pillar, and asked if Lord was present there. Lord Vishnu then emerged as a half lion, half man from the pillar which was neither inside the house nor outside, and the time was evening, neither night nor day. He then killed Hiranyakasyapa thus saving the life of his devotee Prahlada.
5-Vaman Avatar
(short man)
Homo Erectus, Upright, yet short and weaponless (5 million - 2 million years ago)
The fourth lineal descendant of Hiranyakashyap, named Bali, through his devotion and penance defeated Indra, the god of firmament, humbled other gods and extended his authority over the three worlds.The Story of VARAHA Avatar
In VARAHA Avatar, Lord Vishnu incarnates himself as a boar in this world. A demon Hiranyaksha, had prayed for Lord Brahma and got awarded a boon that no beast nor man nor god could kill him. But somehow from the list of beasts the name of boar was missing. This proved to be his lacunae. He then started a campaign of plunder across the worlds. He pushed the world to the Pataal loka, or the under of the sea. He stole the Vedas, the holy scriptures from the Lord Brahma, while he was asleep and performed huge atrocities. To retrieve the Vedas and to save the world the Lord Vishnu assumed the role of a boar and brought out the earth from the under of the ocean, using its two tusks. It then killed Hiranyaksha and retrieved the Vedas from the asura and brought it back to the safe custody of the Lord Brahma.
6-Parsuram Avatar
(parashu=axe, Rama=name of God)
Bronze age; the coming of Ramapithecus; development of first weapons such as axe. Homo Sapiens (350,000-100,000 years ago)
Parsu is the name of an axe-like weapon adopted by this incarnation. Parasuram was a brahmin who manifested himself at the close of the satya-yug. This appearance was for the purpose of defeating the tyranny of the power-drunk kshatriyas. When the kshatriya kings of the earth and their ministers became very corrupt and tyrannical, the goddess Prithvi (Mother Earth) went to Lord Vishnu and prayed for relief. Lord Vishnu answered the prayer and appeared on the earth as a descendant of the great sage Brigu. Parasuram avenged the gruesome murder of his father by a kshatriya king and freed the earth of oppression perpetrated by the rulers by clearing the earth of kshatriyas.The Story of PARASHURAMA Avatar
In PARASHURAMA Avatar, Lord Vishnu incarnates himself as a brahmana (priest) in this world. He was brought in this world to avenge all kshatriyas who had become arrogant and were suppressing the brahmans in the world. He was born to Jamadagni and Renuka, and belonged to the Brighu clan. Parashurama was always carrying an axe presented to him by Lord Shiva of whom he was an ardent devotee. Kartavirya a powerful king, once went to Jamadagni's home when he was out, and after a meal, stole the Kamadhenu cow, which was supposed to give endless quantity of milk.Jamadagni was enraged and he went and killed the king and brought Kamadhenu back. On hearing this, the son of the king came back and killed Jamadagni.Parashurama was enraged at this and went and avenged the death of his father by killing all kshatriyas in 21 battles.
7-Lord Rama Avatar
Lord Rama is one of the most commonly adored gods of Hindus and is known as an ideal man and hero of the epic Ramayana. He is always holding a bow and arrow indicating his readiness to destroy evils. He is also called "Shri Rama". More commonly he is pictured in a family style, (Ram Parivar) with his wife Sita, brother Lakshman and devotee Hanuman who is sitting near Lord Rama's feet The Story of RAMA Avatar
In RAMA Avatar, Lord Vishnu incarnates himself as RAMA, the central character in the epic Ramayan. In the epic, the character RAMA is expected to show the world the characteristics of an ideal person, including ideal son, ideal husband, ideal king and an ideal person. RAMA was incarnated upon this planet to get rid of the asura with ten heads, Ravana, who had been granted a boon by Brahma of immunity from gods, and other celestial beings. Ravana was too vainglorious to be thinking of being vanquished by a man. Hence RAMA was born and Lakshmi, wife of Lord Vishnu was born as Sita, his wife to be in this life. The story of Ramayan, is an exciting nail-biting story of the war raged by Rama against various evil elements of the world and in the end against Ravana.Ramayan epitomises the ideal behaviour of man, with special focus on man-wife relationship, son-father relationship and the rules for ideal governance by a king.
8-Balaram Avataras
Balaram was the older brother of Shri Krishna. He was so powerful that he, single handedly, at a very tender age, killed the great demon, Asuradhenuka, who had the form of a ass. Another demon tried to carry off Balaram on his shoulders, but the young boy beat out the demon's brain with his fist. When Shri Krishna went to Mathura, Balaram accompanied him and supported him till Kamsa was killed by Shri Krishna. He also taught Duryodhan and Bheem, the use of the mace. His chief weapon is ploughshare (hal) and therefore called Haldhar.
9-Lord Krishna &LORD Buddha
Because of his great Godly power, Lord Krishna is another of the most commonly worshipped deities in the Hindu faith. He is considered to be the eighth avatar of Lord Vishnu. Shree Krishna delivered Bhagwad Gita on battlefield to Arjun.
The Story of KRISHNA Avatar
In KRISHNA Avatar, Lord Vishnu incarnates himself as KRISHNA , the central character in the epic MAHABHARATA. In the biggest epic of Indian mythology a myriad of topics are covered, including war, love, brotherhood, politics etc. It is essentially the story of two warring groups of cousin brothers, the PANDAVAs and the KAURAVAs. As a part of the Mahabahrata, during the war KRISHNA, gives a long discourse to his disciple ARJUNA, collectively termed as Bhagvad-Gita.Krishna, during his child-hood was responsible for the killing of Kamsa. Krishna is also considered to be an ultimate playboy who was responsible for charming all gopikaas around him.Unlike Ramayan, Mahabharata deals with more down to earth issues like politics, human nature, human weaknesses, and does not attempt to idealise the characters as in Ramayan
The Story of BUDDHA Avatar
In BUDDHA Avatar, Lord Vishnu incarnates himself as BUDDHA, the ascetic prince who renounced the throne to lead the world on the path of peace. He is the founder of the BUDDHIST religion prominent across the world. In certain sects of Hinduism, he is considered to be a divine incarnation of Lord Vishnu. He was born the crown prince of the Kapilavastu to Suddhodana and Maya. He was named Siddhartha, meaning "All thing fulfilled" by the king. But his mother died soon after his birth but Prajapati, the sister of Maya, brought Siddhartha up. Buddha was saddened by death of living creatures, since his childhood days and used to question: "Alas! Do all living creatures kill each other?" He wasn't happy with any answers that were provided to him and he decided to find out the meaning and the absolute truth and he left his wife and child to a hermit's life in the forest and one day, became the enlightened one. His preaching spawned off the religion of Buddhism now popular across the whole world.
Lord Gautama Buddha.
Gautama Buddha adopted the life of a religious teacher from the age of thirty-five till his death at the age of eighty (c. 486 B.C.). He was a great teacher and had a tremendous following in the provinces of Magadha, Kosala and all the neighboring territories. He defined four noble truths (Arya Satyani
1-The world is full of suffering
2-The desire is the root cause of worldly existence
3-Conquering desire and attachments are the only way to happiness
4-Conquering of desire must be done in the right way.
Buddha explained in detail, the chain of causes which lead to suffering and the means of deliverance from these sufferings. He said that the man is the arbiter of his own destiny, not the gods. He condemned the efficacy of Vedic rites and rituals and challenged the superiority of the Brahmins
10-Kalki Avatar 
The tenth and the last avatar of Vishnu, Kalki, is yet to appear. Kalki will appear at the end of the Kalyuga. This avatar will appear seated on a white horse with a drawn sword blazing like a comet. He shall come finally to destroy the wicked, to restart the new creation and to restore the purity of conduct in people's lives .
The Story of KALKI Avatar
In KALKI Avatar, Lord Vishnu will incarnate himself as KALKI, the machine-man, who will come riding his white horse and with his blazing sword in his hands. This is supposed to be a future avatar of Lord Vishnu. At the end of Kali Yuga (present eon) He will punish all evil doers in this world, destroy this world and recreate a golden age again. KALKI is the last of the avatars of Lord Vishnu.