The deity Vishnu is central to Hindu worship. Among many divine traits, Vishnu incarnates in different forms on earth. In Hindu cosmology, Vishnu takes ten incarnations known as the dashavatara. Dash means ten and avatara means incarnation in Sanskrit. Nine of these incarnations have already taken place and the final one is yet to come. Vishnu assumes these avatars for the purpose of defeating unrighteous forces and establishing righteousness, or dharma. More specifically, dharma is any action that leads towards liberation from the cycle of birth and death (moksha).

These incarnations correspond to different eras or time periods in Hindu cosmology known as yuga. Yuga are cyclical in their origination and dissolution, and there are a total of four yuga before a new cycle begins. In each of the brief descriptions of Vishnu's avatars below, unrighteousness has come to reign on earth, and Vishnu arrives each time in a unique form (either animal, half-human/animal or human) to establish order. The dashavatara are organized according to the yuga in which they took or will take place:

Krita Yuga: 1. Matsya(Fish): Much like the story of Noah in Abrahamic religious traditions, Vishnu takes the form of a fish to save the world from a great flood. 2. Kurma (Turtle): The angels and demons were churning the ocean, trying to create a nectar that would guarantee immortality. They were doing so from the top of a mountain that started to sink. Vishnu takes the form of a giant turtle and lets the mountain sit on his back. 3. Varaha (Boar): The evil demon Hiranyaksha has captured the earth and kept it in the cosmic ocean. Vishnu then takes the form of a boar to save the earth. 4. Narasimha (Half man/half lion): The demon Hiranyakashipu is wreaking havoc but is protected by a special boon that makes him invincible to being killed by both man and animal. This boon also protects him in other conditions that seem to make him completely invincible. Therefore, in this avatar, Vishnu takes the form of half man/half lion and defeats the demon.
Treta Yuga: 5. Vamana (Dwarf): This avatar is the first human incarnation of Vishnu. Bali, another demon, has taken over the three worlds. All the deities appeal to Vishnu who appears disguised as a dwarf. After negotiating with Bali, Vamana then shows his more magnificent form and Bali humbles himself. Because of Bali's humility, Vishnu grants him immortality. 6. Parashurama: Parashurama is believed to have lived through many eras. Vishnu appeared in this form vowing to kill all the male kshatriyas, or members of the warrior caste, who were arrogant and tyrant rulers until he filled the five lakes with their blood. He was eventually stopped by his grandfather, a great sage. 7. Rama: The narrative of this incarnation of Vishnu is found in the great Hindu epic, the Ramayana. Rama is believed to be the most ideal divine hero and is greatly revered. In the central plot of the Ramayana, the evil demon Ravana has abducted Rama's wife, Sita. Rama eventually kills the demon and saves Sita.
Dwapara Yuga: 8. Krishna: Vishnu's avatar as Krishna is the most elaborate story of all the avatars as well as the most widely known and beloved among Hindus. One of Krishna's most significant actions is delivering the Bhagavad Gita to Arjuna, a central figure in the Mahabharatha, before the great battle at the end of the epic. Thereby, Krishna plays a central role in assisting the actors of righteousness in a literal battle against unrighteousness. Krishna is also revered for his vibrant and complex personality. For example, many narratives tell of his mischievousness during childhood and adolescence. 9. Balarama or Buddha: Some consider the ninth incarnation of Vishnu to be the brother of Krishna, Balarama. Others consider it to be the Buddha, the Indian prince who dedicated himself to solitude in the forest and became enlightened. After his enlightenment, he taught and acquired many followers.
Kali Yuga: Kalki: In Hindu cosmology, Kali Yuga is our present era and Kalki is the incarnation of Vishnu that is yet to come in order to combat evil and restore balance. In this avatar, Vishnu will appear in human form, riding a white horse and wielding a blazing sword.

While most Hindu deities are present and active in the life of the worshipper, these narratives of Vishnu's incarnations on earth illustrate ways in which God changes the course of existence on a grand scale. And for Vishnu, this involvement in the fate of humankind is worshipped as a central trait.