According to Hindu mythology, the world then was divided into asuras (demons) and devas (gods). Despite being an asura, Prahlad, son of Hiranyakashyapu, worships Lord Vishnu. Despite many attempts, Prahlad and his devotion never died. Hiranyakashyapu is finally killed by Narsimha Avatara (the fourth Avatara of Lord Vishnu).
Mahabali is the grandson of Prahlad. Mahabali was sent to rule the land of Kerala to curb Indra’s pride. Once Indra’s pride was curbed and Mahabali, a benevolent person who earns people’s love, began to rule all the three worlds, Vishnu as Vamana avatar (the fifth avatar) attended a Yagna that was being conducted by Mahabali.
Mahabali who had inherited love and kindness from Prahlad said he would give any thing that was asked. When Vamana, dressed as a Brahman asked him three feet of land. Shukracharya, a clairvoyant adviced him against it and said it was the lord himself who has asked the three feet of land. Since Mahabali couldn’t go back on his word, he agreed. He tells Shukracharya "Prana (life) and Maana (honour) are like the two eyes of a person. Even if life goes, honour should be protected. Knowing that the person that has come now is the Lord Himself, I should be the most fortunate one as the Lord, who gives everything to mankind, is seeking something from me."
Vamana grew so huge that two feet covered the two worlds.
Mahabali accept to place the third foot on his head. Bartered for immortality and rule of the netherworld, Vamana gives back the control back to Indra.
He is granted a boon to visit his subjects once a year.
Onam is the celebration of this return. Onam is celebrated over a span of ten days with a melange of food, culture, dance, devotion and a flower carpet that embellishes each house to welcome the benevolent Emperor Mahabali.
Onam asham shagallto everyone who celebrates the festival.
P.S: Please correct me if the story is incorrect in any place.
Mythological stories interest me and they teach us values and lessons.
Mahabali teaches us how to be humble and despite knowing he would be destroyed he never moved an inch from his promise and received his due in return.