The dashavtara of Lord Vishnu
Lord Vishnu, the Hindu god of preservation descended on the Earth in ten avatars to restore cosmic order. These ten avatars played a major role in evolution according to Hindu mythologies. As it’s said in the Holy Bhagvat Gita
"Whenever there is a decline in righteous and wherever there is a predominance of unrighteousness. I incarnate on earth"- Bhagavad Gita 4:7.
Here are the 10 avatars or swaroops of Lord Vishnu:
When the world was at the verge of extinction, Manu the first human on Earth was instructed by the gods to rescue the life form on Earth. He chose 1 male and 1 female from each species, plants of different species and loaded them in the ship he had already built, as the whole world was covered in water and there was no land to stay.
A fish(Matsya) came to their rescue. The fish had horns to which the ship was tied. The fish pulled the ship to a small island near the Himalayas where there was land for all the life forms to flourish.
Mandrachala was the mountain used to churn the ocean for the milk of immortality by the asuras. It was used to an extent that it begun to drown. Thus, Lord Vishnu came in the Swaroop of a tortoise called Kurma to carry the mountain.
A demon Hirnyaksha stole the Earth(goddess Bhudevi) and hid her in the primordial waters. Lord Vishnu descended as a boar names Varaha (meaning sacrifice) and rescued her. The battle between Varaha and hirnyaksha is said to have lasted a thousand years. Varaha killed Hirnyaksha and lifted the Earth using his tusks from the ocean and restored its place in the universe.
Hiranyakashipu, a demon had a blessing that he could be neither killed by an animal or a human, neither inside the house nor outside, not on Earth nor in the sky, neither at day nor at night, and not with any weapon. Thus, Vishnu descended in the form of half man and a half lion called Narasimha, killed the demon with his nails at dusk on the threshold of his house and on his thighs.
In treta yug, Bali was the demon king who had captured three different worlds. Thus the gods appealed Lord Vishnu for protection and so he descended in the Swaroop of a dwarf named Vamana. When Vamana approached Bali, Bali promised him to give whatever he asked for. Vamana asked for 3 paces of land and Bali agreed. The dwarf then changed his size to that of a giant. He stepped over heaven first and then netherworld in the second. Bali then realised that Vamana was incarnate of Lord Vishnu and offered his head as the third place for Vamana to step his foot on. He was granted Moksha.
Lord Vishnu took the form of a Brahmin to end the rule of nasty rulers and unchaste women. He played important roles in Mahabharata and Ramayana. He was the teacher of Karna, Drona and Bhishma. He is one of the seven immortals mentioned in the scriptures.
The prince and king of Ayodhya. Ramayana describes the life of Prince Rama. His life depicts the devotion to dharma despite the hardships thrown by life. During his exile, his wife Sita was kidnapped by the demon Ravana. And thus, he had a fierce battle with him and killed him.
In the dwaparyuga, there were so many wars and unrest amongst people. Thus, Krishna was born to kill the demons and provide peace to the world. He was also a very good friend to Draupadi and he gave the lessons of Dharma to the people around him and hence, taught the meaning of true spirituality.
When the world lost understanding and people had a lack of spiritual values, Lord Vishnu incarnated as Buddha to spread self-realization and self-introspection amongst all. He changed the philosophy of Hinduism, away from the philosophies of heaven and hell.
Kalki is the final incarnation of Vishnu expected to appear at the end of Kalyuga. Religious texts tell that Kalki will ride on a white horse with a blazing sword and will kill those with bad intentions.