Lord Shri Hari Vishnu incarnated in every era to protect the religion. Although there have been many incarnations of Lord Vishnu, but among them there are 10 incarnations which find a prominent place. Below are the stories of 10 incarnations of Lord Shri Hari Vishnu i.e. Dashavatar.
1. Matsya (Fish) Avatar:
According to the Puranas, Lord Vishnu had taken the incarnation of Matsya to save the universe from destruction from a the deluge. The story is as follows - King Satyavrat became king in the beginning of Kritayuga. One day King Satyavrat was taking bath in the river. While scooping water from the river he accidentally caught a tiny fish in the palm of his hand. When he saw this, he thought of throwing the fish back into the ocean, but the fish said, "Don't throw me into the ocean, otherwise the bigger fishes will eat me." Then King Satyavrat kept the fish in his water utensil. When the fish grew bigger, the king kept it in a bowl, then in a lake, and within no time the fish became even bigger for the lake.
The king understood that this was no ordinary creature. The king prayed the fish to return to its original form. Hearing the king's prayer, four-armed Lord Vishnu appeared and said that this is my Matsya avatar. God said to Satyavrat –
"Listen King Satyavrat! Doomsday will happen seven days from today. Then with my inspiration a huge boat will come to you. You take the seven sages, medicines, seeds and subtle bodies of living beings and sit in it, when your boat starts wavering, then I will come to you in the form of a fish. At that time, you tie that boat to my horn with the help of Vasuki - the snake. Soon after I will answer your questions and due to which my glory, which is known as Parabrahma, will be revealed in your heart."
For countless years darkness covered the worlds and together they wandered across the stormy wastes waiting for the waters to subside. During their journey Lord Vishnu-Matsya instructed King Satyavrata and the sages in the spiritual knowledge of the Vedas. Then when the time came, Lord Vishnu in the form of a fish preached Tatvgyan to King Satyavrat, which is famous by the name Matsyapuran.
2. Kurma (Tortoise) Avatar:
Lord Vishnu took the incarnation of Kurma (tortoise). Kurma is the tortoise incarnation of Lord Vishnu, who appeared to help the devas (demigods) and asuras (demons) in the churning of the cosmic ocean of milk (Ksheera Sagara) to obtain the nectar of immortality. The story is as follows - Once, the demigods and the demons both wanted to get the Nectar of Immortality. Whoever drank this nectar would be invincible. On the advice of Lord Vishnu, they made a pact and agreed to co-operate together to get it. To churn the ocean they would have to use the golden mountain, Mandara, as a churning rod. With great difficulty and Vishnu’s help they managed to bring Mount Mandara to the Milk Ocean. They used Vasuki, the giant serpent, as a rope. Wrapping him round the mountain, the demons took hold of his head and the demigods took his tail.
But since there was no base beneath Mandarachal, it started sinking into the ocean. Seeing this, Lord Vishnu took the form of a huge Kurma (tortoise) and became the support of Mandarachal in the ocean. Mandarachal started rotating rapidly on the huge back of Lord Kurma and thus the churning of the ocean was completed. The first thing the churning produced was a deadly poison which threatened the whole world. This was drunk by Lord Shiva to save everyone. Many valuable items also emerged from the ocean, including the goddess of wealth, Lakshmi, and the nectar of immortality.
3. Varaha Avatar:
Lord Vishnu took the third incarnation in the form of Varaha. The story related to Varaha incarnation is as follows - In ancient times, when the demon Hiranyaksha took away the earth and hid it in the cosmic ocean, then Lord Vishnu appeared in the form of Varaha from the nose of Brahma. Seeing this form of Lord Vishnu, all the gods and sages praised him. On everyone's request, Lord Varaha started searching for the earth. With the help of his snout he located the earth and after going inside the cosmic ocean and placing it on his teeth he brought the earth out.
When the demon Hiranyaksha saw this, he challenged the Varaha form of Lord Vishnu for war. There was a fierce battle between the two. At last Lord Varaha killed Hiranyaksha. Lord Varaha defeated Hiranyaksha and lifted the earth out of the cosmic deep ocean using his tusks, restoring it to its proper place in the solar system.