Demoness Ajamukhi was the sister of powerful demon Surapadman, who was vanquished by Murugan. The goat-faced demoness had two sons from Sage Durvasa. The way in which she got the sons and their nefarious activities are mentioned in the below story.
Demoness Ajamukhi went around killing handsome men. She also found pleasure in destroying the ashrams of the rishis.
Once she chanced upon the ashram of the powerful Sage Durvasa. The sage was deep in meditation. Ajamukhi wanted to have children from the sage. She tried to entice the sage but the angry sage declined her advancements and angrily told her he will not accept her as his wife.
Suddenly, Ajamukhi tightly embraced Sage Durvasa. The sage struggled to get out from the embrace and in this process two sons emerged from Ajamukhi.
She named the two sons, Vatapi and Vilvalan.
The sons requested their father to grant them the power he had accumulated through his tapas. Durvasa declined and told them to ask any other boon. The two brothers were adamant and threatened to kill their father.
A furious Durvasa cursed them to be killed by Sage Agastya and returned back to his penance.
On the advice of Ajamukhi, Vatapi and Vilvalan propitiated Brahma. But Brahma did not appear before the demon brothers. Finally, Vilvalan killed his brother Vatapi and threw the dead body into the sacrificial fire. Brahma was forced now to appear before Vilvalan. As first boon the demon asked his brother be brought back to life. Vatapi was brought back to life in the form of a goat.
The demon next asked a strange boon – that his brother should be restored back to life each time he killed him. Brahma agreed to the strange boon and disappeared.
The demons went around the earth disturbing saints and innocent people. Vilvalan would take the guise of a sage and would invite other rishis to his house. He would then kill his brother and serve him to the unsuspecting rishis. Once the sages had eaten the served food, Vilvalan would restore his brother back to life. Vatapi would appear burst opening the stomachs of the sages and killing them.
The brother tried the same trick on Sage Agastya. But the powerful sage realized their trickery. Immediately after eating the food, the sage chanted the mantra for the food to be digested completely. Vatapi was completely digested by Sage Agastya. An angry Vilvalan tried to attack the sage but he was killed by the power of the penance of the sage.