Kurma (Sanskrit: कुर्म) was the second Avatar of Vishnu. In this Avatar, Vishnu takes the form of a tortoise to help the Devatas get the Amrita and regain the prowess they lost due to a curse. Like the Matsya Avatar, this Avatar also belongs to the Satya yuga.
Devas and asuras are cousins. But this has not stopped them from going into many wars with each other. Once upon a time the Devas seemed to be on the verge of being defeated by the asuras. Bhagavan Vishnu suggested a way to achieve victory. He told the Devas that they should challenge their sworn enemies – asuras – to the Kshir Sagar where both the teams would churn the sea. The team that emerges victorious will have right over the nectar that is produced from the churning of the ocean. This nectar will give the victorious team an upper hand over the other.
Some Devas struck a deal with greedy asuras and convinced them by promising them some nectar. Mandarachal mountain was brought to the sea and tied with Vasuki snake to churn the sea. But the heavy mountain started sinking into the sea. Supreme Lord Vishnu in his second incarnation, in the form of a turtle Kurma, came to their rescue and supported the mountain on his back.
As soon as the bowl of amrita, the nectar of immortality was out, the asuras grabbed it. Then Lord Vishnu took the form of an apsara, a beautiful maiden, and seduced the asuras into letting her distribute the nectar and also to abide by her order of distribution. As soon as the devatas were served the maiden disappeared thus totally deceiving the asuras and making them totally weak.
Devas chased the Asuras away from the nether regions of the universe and peace returned to the earth.