In the ongoing saga of battles ensued between Devtaa and Daitya, once Devtaa were defeated in that battle and the demons headed by Daitya Raaj Bali gained control of the Universe. Devtaa sought out the help of Lord Vishnu, who instructed them in the art of diplomacy. He asked Devtaa for an alliance with Daitya to jointly churn the ocean for the nectar of immortality and to share it among them. And during this process He would help them to obtain Amrit, which would empower them to defeat Daitya.

All kinds of herbs were cast into the Ksheer Saagar (milky ocean) and using Mandar mountain as the churning rod and Vaasuki Naag as the churning cord, all started to churn the ocean. This churning was so arduous that Lord Vishnu Himself interceded in so many ways to aid the Devtaa. He was present as Lord Ajeet pulling the churning cord on the side of Devtaa, as a Koorm (or Kashchap or Kachchhap or Tortoise) to support the great Mandar mountain which was shaking too much, and He Himself sat atop the Mountain infusing Devtaa and Vaasuki Naag with energy. Many great beings and objects came out from the ocean. Some of them were taken by Devtaa, while others were taken by Daitya, yet some others were taken by Rishi. (see the whole list of things coming out of the ocean)

First came out the Kaalkoot Vish (poison) which Shankar Jee drank for the welfare of the Universe. Then came out Surabhi cow who was taken by Rishi; then came out Uchchshraivaa horse who was taken by Daitya Raaj Bali; then came out Airaavat elephant which was taken by Indra; then came out the Kaustubh Mani which was taken by Vishnu; then came out the Paarijaat tree which was planted in Indra's garden Nandan Van; then came out Apsaraa who were taken by Indra; then appeared Lakshmee Jee, the goddess of fortune. She married Vishnu Jee. After that came out Vaarunee Devee who was taken by Daitya; and in the last came out Dhanvantari carrying the Kalash (pitcher) of Amrit.

As soon as the Amrit came out, both Devtaa and Daitya rushed to take it from Dhanvantari's hands. As Daitya were stronger than Devtaa, they snatched the Kalash from Dhanvantari's hands and ran to drink it. Immediately Vishnu appeared as Mohinee (the most beautiful and enchanted woman) - the 14th Avataar of Vishnu, and took that Kalash from Daitya's hands tactfully. Then She distributed Amrit to Devtaa and liquor to Daitya.

All Daitya were happy with what they were receiving from Mohinee, but Raahu Daitya knew Mohinee's tactics - that She was giving Amrit to Devtaa and only liquor to Daitya, so he assumed Devtaa's form and sat in the line of Devtaa between Soorya and Chandra. When Mohinee came to give Amrit to Devtaa She gave some to Raahu also. As Raahu drank it, Soorya and Chandramaa identified him as Daitya and reported this to Mohinee. Mohinee immediately cut his neck with Her Chakra, but She was a bit late and till then Raahu had already gulped some Amrit. He had become immortal. As he was cut in two pieces, he did not die, rather his both parts remained alive.

Since Soorya and Chandra complained to Mohinee about him, he became the enemy of both of them and has been after them since. Whenever he gets opportunity he tries to swallow Soorya (on New Moon or Amaavasyaa day) and Chandra (on Full Moon or Poornimaa day), which we call Soorya Grahan (Solar Eclipse) and Chandra Grahan (Lunar Eclipse) respectively. Later Brahmaa Jee gave his both parts the status of planet - Raahu (to his head) and Ketu (to his trunk).

Devtaa drank the Amrit and became invigorated with energy. Thereafter, they fought with Daitya and defeated them.

[In this event Bhagavaan Vishnu incarnated two times - first as a Koorm or Kashchap or Kachchhap (Tortoise) and later as a beautiful maiden Mohinee. ]