It is believed “Avatar” or divine descendent refers to the Supreme Divine taking a brief human form for his own purposes, which are considered to refer to the welfare of the world which is His own creation. Potentially, Jiva in every being is in the sense an Avatar, which is best expressed by the Mahavakya, Tat Tvam As.
Bhagwan Vishnu have already incarnated on earth 23 times, while the 24th avatar is yet to be known as 'Kalki Avatar'. Out of these 24 avatars, 10 avatars, called as Dashavatar, are considered to be the main incarnations of Vishnu. This is Matsya avatar, Kurma avatar, Varaha avatar, Narasimha avatar, Vamana avatar, Parashuram avatar, Rama avatar, Krishna avatar, Buddha avatar and Kalki avatar. Of all the Avatars, Shri Krishna alone is considered a Purna Avatar, a direct and complete representation of the Supreme Divine Himself.
Matsya a Fish, Kurma a Tortoise, Varaha a Boar, through Nrsimha, a half-lion Man, making a transition to the human sequence of Vamana, Parasurama, Rama, Krishna and Kalki making the ten accepted by the Vaishnava tradition.
Stories of 24 Avatars are as under: