There are beautiful stories woven around this festival, which is over 500 years old. The most popular legend is about King Mahabali. A long time ago an Asura king named Mahabali ruled Kerala. He was dearly loved by his subjects and was known to be a just and wise ruler. His popularity soon spread far and wide. Mahabali, however, incurred the wrath of the gods when, besides earth, he extended his rule to the heavens and the nether world. Indra, the king of gods, did not appreciate the growing power of the asura king. The gods approached Lord Vishnu - the preserver in the Hindu trinity -- to help them out of the situation and to curb the growing power of the asura king. Lord Vishnu in the guise of Vamana (a brahmin dwarf) approached Mahabali for alms. Mahabali being a very generous man told the Vamana to ask for anything. The Vamana asked for three paces of land and the king agreed to it. Immediately the Vamana increased his size, till he grew as big as the universe. And with one step he covered the earth. With the second step he covered the heaven and the nether world. He did not have any land to place the third step. Mahabali, who was a man of principles, offered his head as the third step. And the Vamana placed the third step on Mahabali's head and sent him to nether world. However before placing the final step, Mahabali was granted a boon. Mahabali was allowed to return to his country once a year and visit his people. And Onam is the day when Mahabali comes to visit his people. In memory of the happy days of Mahabali's rule, a grateful Kerala celebrates his annual homecoming with all the pomp and grandeur it can command.

Another legend has it that once about 10 kilometres up the river Pampa from Aranmulla, the head of the Katoor Mana, a Nambudiri family, offered prayers and waited to feed a poor man. After a long wait he began to pray to Lord Krishna. When he opened his eyes there stood before him a poor boy almost naked. The Nambudiri took him to the river, gave him a bath, a new set of clothes and a splendid meal. Much to the surprise of the Nambudiri, soon after eating the meal the boy disappeared. The search for the little boy led the Nambudiri to the Aranmulla Temple. But after a brief encounter the boy disappeared again. The Nambudiri thereafter brought the food to Aranmulla Temple every year during Onam. The glory of those ancient times is recaptured in a popular folk song, which is sung all over Kerala: And the song goes like this:

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