Onam is a four-day harvest festival celebrated in Kerala. It falls in the Malyali month of Chingam, marking the end of the life-giving monsoon and the advent of spring.

Mythologically, the event celebrates the annual visit of King Mahabali. According to a legend in Vishnu Purana, Mahabali was a demon king, and through severe penance had gained dominion over the three worlds. He was an able and just ruler and his people respected him. The gods however, shorn of their powers and deprived of their abode and the spoils from sacrifices performed on earth, asked Vishnu for help. He agreed, and took his fourth incarnation of Vamana, the dwarf. Accordingly, he was born to Sage Kashyapa and his consort Aditi. When he attained maturity, he went to the court of Mahabali, who was in the midst of a sacrifice. The virtuous Bali saw the Brahmin and immediately asked him what he desired. Vamana begged for as much land as he could encompass with three steps. Bali agreed to the humble request but as soon as the sacrificial water was poured on Vamana’s hands, he became a giant. With one step he covered the earth, with the second step the heavens. As there was no place to claim his third step, Bali offered his head as a resting ground. Vishnu put his foot on Bali ’s head and pushed him down to the netherworld.

However, in recognition of his virtues, Vishnu made him king of the Asuras. At Bali ’s request, Vishnu allowed him to return to earth to visit his people once a year .It is believed that Mahabali visits his people in Kerala during Onam.