In Hinduism, an avatar means the form of a deity and usually refers to an incarnation of God or His aspects such as Vishnu on planet earth either as a man or an animal or some mythical creature. The term avatar literally means "descent" in Sanskrit. The concept of avatars came into vogue in later historic periods of Itihas and Puranas (scriptural mythologies). The avatars are believed to descend to earth based on the needs of time, protect the good, destroy the evil, and restore righteousness. The doctrine appears in the Bhagavadgita in the words of Lord Krishna to Arjuna: “Whenever there is a decline of righteousness and rise of unrighteousness then I send forth Myself”. The number of Vishnus avatars is ten, which are Matsya (fish), Kurma (tortoise), Varaha (boar), Narasimha (half man, half lion), Vamana (dwarf), Parashurama (Rama with the axe), Rama (hero of the Ramayana epic), Krishna (the divine cowherd), Buddha, and Kalkin (the incarnation yet to come). However, the number of Vishnus avatars is sometimes extended or their identities changed, according to local preferences.