In Hinduism, an avatar is a physical representation of a deity in the mortal world in the form of a beast or a human. Avatars are a central component of Vaishnavism, the worship of Vishnu, who has ten avatars that descend to restore cosmic order to the world. Of his ten avatars the most highly regarded are Buddha, Rama and Krishna, with the latter two being subjects in the epics the Ramayana and the Bhagavad Gita (A section of the larger Mahabharata).
Of the avatar stories, my personal favorite is the one of Narasimha. In a quest for vengeance against Vishnu, who killed his brother, the rakshasa king Hiranyakashipu underwent years of penance and meditation to be granted a favor by the god Brahma. He asks for invincibility, but when Brahma refuses he adjusts his phrasing: he cannot be killed by day or night, inside a building or outside, by man or beast, by weapon living or inanimate. Brahma agrees to this one. As Hiranyakashipu’s son Prahlada grows up he becomes a worshiper of Vishnu, which greatly angers Hiranyakashipu. When Prahlada claims that Vishnu is the omnipresent supreme being Hiranyakashipu points to a nearby pillar and asks “Is Vishnu in this pillar?” When Prahlada replies that he is, Hiranyakashipu smashes the pillar with his mace. Vishnu appears from the ruins in the form of Narasimha: half man, half lion, but neither man nor beast. Using his claws, he kills Hiranyakashipu on the threshold of his home at the hour of dusk.