Long ago, Parasara muni had built an ashram and was offering sincere prayers. About this time, the milky ocean had been churned and the amrutham thus obtained had been distributed by Lord Vishnu to devas and rishis. Parasara muni, however, wanted to save some of it, so his disciples as well as the trees and animals in his ashram would also benefit. When he took some the amrutham back to his ashram, Indra cautioned that it would be unwise as the demons may come to know about it and the amrutham may be lost. Parasara muni, assured him, that he would protect the amrutham. He took some of it and mixed it in the pond near the ashram. During the course of time, there was a sever famine and all areas were affected except the area surrounding Parasara muni's ashram. Three demons by name Tanjakan, Dantakan and Tarakan, came to know about the ashram and the amrutham mixed in the pond over there. They went to Parasara muni's ashram and partook of the water from the pond. Subsequently they gained strength along with evil thoughts and habits. Soon they started giving trouble to the rishis and their disciples.

Parasara muni prayed to Lord Siva, who appeared before him and asked him to get help from Lord Vishnu. He however, sent Chandika devi to help him keep the demons at bay until the time Maha Vishnu found a solution to the problem. Chandika Devi went ot Parasara muni's ashram and fought with the demons, while the muni did sever penance to Lord Vishnu. Each time, when Chandika Devi killed a demon, others would go and sprinkle the pond water on them, thus bringing them back to like. So, it appeared to be an endless fight. In the meantime, Lord Vishnu appeared before Parasara muni, and reminded him of the dangers of taking the amrutham to earth from the milky ocean. He then separated the amrutham from the tank, and thus the demons were defeated as they could not regain the energy from drinking the pond water any more.

Having taken care of the amrutham in the pond, Lord Vishnu, then turned to Tanjakan, who let loose all his weapons on Perumal, with no use. Then turned into an elephant and tried to attack Perumal, who immediately, took the form of Narasimha, took the demon by his hair and was about to kill him. At this time, the demon realized that his end was near and requested Perumal:

O Lord! You have taken the form of Narasimha to just destroy me. I pray that you continue to stay here and enable the devotees to see You in the same Narasimha roopa in this Place.

Seeing that Tanjakan was killed, other demon, Dantakan started running. Perumal took the Varaha roopa, chased and killed him. Meanwhile, Chandika Devi succeeded in killing Tarakan. Vishnu is said to have conferred Her the tittle Eka Vira.

It is said that Tanjakan was the son of Manu. Once Manu, a great Vishnu devotee, was in meditation and did not wish to be disturbed. A rishi came to his ashram to meet him and his son did not pay him the required respect. So the rishi went back to his ashram. When Manu came to know about this, he cursed his son would become an asura. Upon his wife's request, he lessened the curse by saying that he would be killed only by Vishnu and would attain moksha at that time.








Source:
1. 108 Vasihnavaite Divya Desam by Miss M. S. Ramesh.