Vaasuki Naag was taking care of his sister Jaratkaaru very carefully and was on the look out for Jaratkaaru. He had sent his snakes all around in search of Jaratkaaru. Jaratkaaru was a great Brahmchaaree. Once he saw his ancestors hanged upside down in a well tied with a rope which was cut slowly. Anytime it would cut and his ancestors would fall in a dark well. His ancestors told him to marry and produce a son so that they could be saved. He said to them - "I would not marry for myself, I would marry only that girl who will be bearing the same name as mine. Besides I will accept her only when her friends or relations will give her to me as a gift, because who will give his daughter to a poor man like me. But if my three conditions are met, I will surely marry and raise a son for your sake."

So Jaratkaaru wandered around but could not find a wife. So one day he went in a forest and prayed for a wife three times in a faint voice saying, "My ancestors are in grief. They have asked me to marry, so I am roaming around in search of a wife who has been given to me in alms. She should bear the same name as mine and whom I will not maintain." Now those snakes whom Vaasuki had sent around to look for a man who was bearing the same name as his sister (Jaratkaaru) were hearing this. They immediately went to Vaasuki and informed him about this. Hearing this Vaasuki adorned his sister with beautiful clothes and ornaments and went to the forest and gave her to him in alms, but the Rishi did not accept her at once. He asked Vaasuki his sister's name and said that he would not maintain her. Vaasuki agreed and married his sister to him.

They started living there happily. The Rishi said to his wife - "You should never say or do anything which is against my liking, otherwise I will leave you and go away from here." His wife got very sad hearing this but said - "Be it so." And that lady started working for him with the wakefulness of a dog, timidity of a deer, and knowledge of signs possessed by crow. After a while she got pregnant.

One day, Jaratkaaru slept in his wife's lap very tired. Evening fell and Rishi's wife became feared for the loss of her husband's virtue. "What should I do? The alternatives are loss of virtue, and his anger." Deciding what she had to do, she softly tried to wake him up - "Get up, the Sun is setting." Jaratkaaru got angry at this and said - "You have insulted me, I will go where I have come from. The Sun cannot set when I am asleep." Rishi's wife trembled and said - "I did not mean to insult you, I just woke you up so that your virtue is not lost." Jaratkaaru said - "I am leaving you now. I lived happily with you. When I am gone tell your brother that there is no need to grieve for me."

Lady Jaratkaaru said - "The objective for which I was given to you has not been fulfilled yet, what shall I tell my brother? The child to remove the curse of our mother has not yet born. Their welfare depends on the child born from you. Why do you leave me while I am faultless?" Jaratkaaru said - "O fortunate one, The child you have conceived is very virtuous and knows all Ved." Saying thus he went away to do penance. In due course of time a son was born to Jaratkaaru and he was brought up in Naag's house. He studied Ved from Maharshi Chayavan. He was named Aasteek.

So when Janamejaya did Sarp Yagya, Aasteek arrived there and stopped it to save Naag's lives.

[From Mahaabhaarat, Aadi Parv-3]