In Indian mythology, the demons were older than their half-brothers, the Gods.
The Gods and the Demons knew that they could gain the Amrit, the Water of Life, if they churned up one of the seven oceans that, ring beyond ring, encircles the worlds. They came down to the Ocean of Milk. They took the Mountain Mandara for a churning-pole and the hundred-headed serpent Vasu...ki for a churning-rope.
For a thousand years the Gods and the demons churned the Ocean of Milk. All the time Vasuki, the serpent, from his hundred heads spat venom. The venom bit into the rocks and broke them up; it flowed down, destroying the worlds of Gods and men. Then all creation would have been destroyed in that flood of venom if it had not been for the act of Shiva
Shiva took up the venom in a cup and drank it. His throat became blue with that draught of bitterness.
Still they churned.
And then there appeared the sage Dhanvantri, and in his hands was the cup that held the Amrit, the Water of Life. The demons strove to seize it. They almost overpowered the Gods in their efforts to seize the Amrit. Then Vishnu changed himself into a ravishing form; he seemed to be the loveliest of the nymphs of Heaven. The demons went towards where the seeming nymph postured for them. Even as they fought amongst each other for the maiden, the Gods took the cup, and, sharing it, they drank the Amrit.
And now they were filled with such vigour that the demons could not overpower them. Many they drove down into hell. That was the beginning of the wars between the Gods and the Demons…wars that went on for ages