Hindu mythology does not often have a consistent, monolithic structure. The same myth typically appears in various versions, and can be represented differently across socio-religious traditions. These myths have also been noted to have been modified by various philosophical schools over time and particularly in the Hindu tradition. These myths are taken to have deeper, often symbolic, meaning, and have been given a complex range of interpretations.
Many of these legends evolve across these texts, the character names change or the story is embellished with greater details, yet the central message and moral values remain the same. According to Wendy Doniger,
Every Hindu epic is different; all Hindu epics are alike. (...) Each Hindu epic celebrates the belief that the universe is boundlessly various, that everything occurs simultaneously, that all possibilities may exist without excluding the other. (...) There is no single basic version of a Hindu epic; each is told and retold with a number of minor and major variations over the years. (...) Great epics are richly ambiguous and elusive; their truths cannot be filed away into scholar's neat categories. Moreover, epics [in Hinduism] are living organisms that change constantly. (...)
Hindu epic shares the creative principles and human values found in epic everywhere. However, the particular details vary and its diversity is immense, according to Doniger. The Hindu legends embed the Indian thought about the nature of existence, the human condition and its aspirations through an interwoven contrast of characters, the good against the evil, the honest against the dishonest, the dharma-bound lover against the anti-dharma bully, the gentle and compassionate against the cruel and greedy. In these epics, everything is impermanent including matter, love and peace. Magic and miracles thrive, gods are defeated and fear for their existence, triggering wars or debates. Death threatens and re-threatens life, while life finds a way to creatively re-emerge thus conquering death. Eros persistently prevails over chaos.
The Hindu epics integrate in a wide range of subjects. They include stories about how and why cosmos originated (Hindu cosmology, cosmogony), how and why humans or all life forms originated (anthropogony) along with each's strengths and weaknesses, how gods originated along with each's strengths and weaknesses (theogony), the battle between good gods and bad demons (theomachy), human values and how humans can live together, resolve any disagreements (ethics, axiology), healthy goals in stages of life and the different ways in which each individual can live (householder, monk, purusartha), the meaning of all existence and means of personal liberation (soteriology) as well as legends about what causes suffering, chaos and the end of time with a restart of a new cycle (eschatology).
A significant collection of Vaishnavism traditional reincarnations includes those related to the avatars of Vishnu. The ten most common of these include:
Matsya: It narrates a great flood, similar to one found in many ancient cultures. The savior here is the Matsya (fish). The earliest accounts of Matsya mythology are found in the Vedic literature, which equate the fish saviour to the deity Prajapati. The fish-savior later merges with the identity of Brahma in post-Vedic era, and still later as an avatar of Vishnu. The legends associated with Matsya expand, evolve and vary in Hindu texts. These legends have embedded symbolism, where a small fish with Manu's protection grows to become a big fish, and the fish ultimately saves earthly existence.
Kurma: The earliest account of Kurma is found in the Shatapatha Brahmana (Yajur veda), where he is a form of Prajapati-Brahma and helps with the samudra manthan (churning of cosmic ocean). In the Epics and the Puranas, the legend expands and evolves into many versions, with Kurma becoming an avatar of Vishnu. He appears in the form of a tortoise or turtle to support the foundation for the cosmos and the cosmic churning stick (Mount Mandara).
Varaha: The earliest versions of the Varaha or boar legend are found in the Taittiriya Aranyaka and the Shatapatha Brahmana, both Vedic texts. They narrate that the universe was primordial waters. The earth was the size of a hand and was trapped in it. The god Prajapati (Brahma) in the form of a boar (varaha) plunges into the waters and brings the earth out. In post-Vedic literature, particularly the Puranas, the boar mythology is reformulated through an avatar of god Vishnu and an evil demon named Hiranyaksha who persecutes people and kidnaps goddess earth. Varaha-Vishnu fights the injustice, kills the demon and rescues earth.
Narasimha: The Narasimha mythology is about the man-lion avatar of Vishnu. He destroys an evil king (Hiranyakashyapu), ends religious persecution and calamity on Earth, saves his devotee (Prahlad) from the suffering caused by torments and punishments for pursuing his religious beliefs, and thereby Vishnu restores the Dharma.