King Sutapa and his wife Prishni prayed to Lord Brahma for a child. Lord Brahma, with the consent of Lord Maha Vishnu, gave the king an idol of Lord Sri krishna given to him by Lord Maha Vishnu himself. It is believed that by the grace of this idol Lord Brahma was able to fulfill his task of creation. When Lord Maha Vishnu appeared before the King and the queen in answer to their prayers, they prayed to the Lord for a son like Him. As they repeated it thrice, the lord told them that they would have to take three births (janmas) and that in all their three births he would be born to them. In due course the Lord was born to them. In their first birth, He was born to them as Prishnigarbhan, who taught people the importance Of Brahmacharya and its great power. In their second birth, they were born as King Kashyap and Aditi and the Lord took the avatara of Vamana and was born as their son. In their third birth, they were Vasudeva and Devaki, parents of Lord's avatara, Sri Krishna.

Lord Sri Krishna got the idol from his father and worshipped it at his Capital Dwaraka. Before the conclusion of his incarnation as Krishna, the Lord told his Devotee and Minister Uddhava that the image would come floating in the sea which would soon engulf Dwaraka. Udhava was asked to request Brahaspati, the Guru of the Gods, to install the image at a suitable place. Accordingly when the image came floating Brihaspati (Guru) along with Vayu (the God of wind), carrying the idol, set out in search of a sacred place. They met Parasurama (an earlier avatara of Lord Vishnu) in Kerala, who was on his way to Dwaraka to bring the very same idol. Parasurama led them to a beautiful lake full of lotus flowers. Lord Shiva was doing penance there and he told Guru and Vayu to install the idol together at a spot near the lake and that the site should be known as "GURUVAYUPURA". Lord Shiva and Goddess Parvathi left for Mammiyur, on the opposite bank of the lake.

The present tank called "Rudratirtha" is only a miniature of the original lake. When devotees go round the Krishna temple, from a certain spot, they look in the direction of Mammiyur and pray to Lord Shiva. Vishwakarma, the architect of the Gods, built the Sri Krishna temple at the instance of Guru and Vayu. This is the legend told by sage Dattatreya to King Janamejaya, son of Parikshit (as narrated in the Mahabharatha). King Parikshit died of cobra bite due to the curse of a sage. His son King Janamejaya performed a sacrifice in which thousands of innocent reptiles were killed. As a result of their curse, he was affilcted by leprosy. On sage Dattatreya's advice, he went to Guruvayur and worshipped Sri Guruvayurappan in the company of sage Atreya. He prayed with intense devotion for 41 days. He dreamt one night, that the Lord's tender hand was stroking him. Next day, when he woke up, he found that there was no trace of leprosy on his body.