In this sthalam, all the devars along with Nandhagarishi was given the prathyaksham of Sriman Narayanan. Since all of them gathered (koodi) all together, this sthalam is called as “Thirukkoodaloor”.
After coming to this sthalam only, the River Cauvery regained its speciality and holyness. Koodal + oor Koodaloor. Koodal means joining (merging) together at the same place. Since, Cauvery is coming together in this Kshetram, this Kshetram is also called as “Sangama Kshetram”. Sangamam means joined together.
As per Hindu mythology, demon Hiranyaksha fought with mother earth and went underground, called Patala. Vishnu was born as Varaha, an avatar in the form of a boar to pierced underground. He split the earth into two parts and brought the two back at Srimushnam. Thirumangai Azhwar quotes the incident and calls the village as Pugunthaan Oor, meaning the place where Vishnu went inside the earth. Since Vishnu protected the world here, he is called Jagath Rakshaka Perumal (in Tamil as Vaiyam Katha Perumal). The gap seen in the sactum close to the image of Jagath Rakshaka is believed to be the centre point of earth and all devas came together to worship him. Since it brought all of them together, an act referred in Tamil as koodal, the village is called Thirukoodalur.
As per Hindu legend, King Ambarisha who immersed himself in the worship of Vishnu, failed to strengthen his army and lost his kingdom. While doing worship, he also did not observe the sage Durvasa who went along his way. The sage got irritated and cursed the king. The king went to Vishnu for rescue, who sent his discus to chase the sage. The sage surrendered to Vishnu and begged pardon. The king Ambarishan is believed to have built the temple and hence the presiding deity is also called Ambarisha Varadhar at this place.
Once upon a time, all the Devas along with Nandhaga Rishi prayed for a dharshan to Lord Vishnu at Thirukkoodaloor – Sri Aaduthurai Perumal Temple. Impressed with their Poojas, the Lord appeared before them and gave a splendid Dharshan. Everybody requested that the Lord kill the Asura Hiranyaaksha.
Lord Vishnu was very happy with their Poojas and decided to kill the Asura Hiranyakshaka. Lord Vishnu cut open the earth, killed the Asura and reappeared, with Goddess Lakshmi, as Varaaha Moorthy (one of the 10 Avathaarams of Maha Vishnu) at SriMushnam.
As all of the Lords and Devas came together at Thirukkoodaloor – Sri Aaduthurai Perumal Temple and prayed to the Lord requesting for protection, this place has come to be called Koodalur (where people come together). The Lord who protected the village from the Asura was named as JagathRakshgan meaning “One who protects the World”.