Janmajeya, Utanka and Takshaka were mere pawns in the hands of fate. The snake sacrifice had been ordained aeons ago as a result of sibling rivalry between Kadru and Vinata. Kadru and Vinata were daughters of Daksha and were married to the sage Kashyap along with their other sisters.
Kadru desired to have a thousand snakes as sons. Vinata wanted only two sons, but the two to be more powerful than Kadru's offspring in every way. In due course Kadru delivered a thousand eggs, which hatched into splendid snakes. Takshaka was the fourth of these, the first three being Sesha, Vasuki and Airavata. However Vinata's two eggs remained as they were. Burning with jealousy, she broke open one egg. Inside was a bird with only the upper half developed. The bird cursed his mother because her impatience had been his undoing. Vinata would be enslaved. She should let the second egg hatch naturally. The offspring from that egg would free her. If she tampered with the second egg she would be a slave forever. This bird, named Arun, became the charioteer of the sun.
Uchchaisravas was the illustrious horse that had emerged from the churning of the oceans. Kadru inquired of her sister what was the colour of the horse's tail. When Vinata replied that the tail was white, Kadru laid a bet with her. "If the tail has any black in it you will become my slave, if it is all white I will become yours," she said. Since Vinata knew that the tail was all white she readily accepted the wager.
That night Kadru instructed her snakes to hide in the tail of Uchchaisravas so that it appeared black when the two sisters went to settle their bet the next day. They refused to obey their mother. It was then that Kadru proclaimed a curse on them saying that all snakes will die in a sacrifice that will be conducted by Janmajeya. But Kadru was bent on enslaving her sister. She found someone else to do her bidding. Vinata lost the bet and was enslaved. In due course the second egg hatched and from it emerged Garuda, the king of birds and a serpent-eater. Garuda then set his mother free. But that is another story.
The serpents had inherited their evil nature from Kadru. They had refused to abet their mother in enslaving their aunt, not out of goodness of heart, but to spite Kadru. Now the threat of extinction loomed large on them. The eldest, Sesha, immediately realised that he had no future with his brothers. He left them and practised severe penances. He made pilgrimages to all the holy places. Brahma was impressed with Sesha's austerities. He asked him the reason for his newfound devotion. Sesha expressed his desire to leave his family forever and lead a pious life. Brahma the Creator then gave Sesha the responsibility of holding the earth in a steady position.
The responsibility of countering Kadru's curse now came to Vasuki. He called a council of all his brothers to discuss the problem. Several suggestions were voiced. One suggested that they should assume the form of a Brahmin more learned than Utanka and advise Janmajeya to abort his intention of performing the sacrifice. Another argued that assuming the form of his ministers would be better. Yet another suggested that one of them should bite Utanka so that the poison kills him and he cannot perform the sacrifice. "Why not bite the king himself?" a fourth ventured. Vasuki did not agree with them. "We cannot counter this curse with evil," he said. "Let us consult our father, the sage Kashyap."
A snake named Elapatra then spoke. "I have overheard a conversation between Brahma and some demi-Gods, who were questioning the wisdom of our mother's curse. Brahma told them that the race of snakes had multiplied beyond control. Also many of the snakes were a menace to humankind and needed to be exterminated. Therefore he had not intervened in Kadru's curse. The demi-Gods questioned further. But there are many species of snakes that do not cause anyone any harm they informed Brahma. Why should these species be destroyed they wanted to know. Brahma told them that he was aware of this. He had taken steps to ensure that the good snakes would be saved. The man who would be the instrument in this would be shortly born to a sage named Jaratkaru. The demi-Gods were aghast. Jaratkaru was an avowed bachelor. Brahma read their thoughts and asked them to wait and watch the events unfold."
Vasuki ended the meeting. "Those of you who want to be saved better change your ways," he cautioned his brothers. After the snakes had dispersed Elapatra took Vasuki aside. "Brahma had mentioned that you will play an important role in the coming drama."