King Maha Bali is known to all the Keralites through their most important festival of the year called Onam. But not everyone knows that Maha Bali is behind the origin of Rakhi a.k.a. Raksha Bandhan which is a predominantly North Indian festival.
It is a well known story that Lord Maha Vishnu sent Maha Bali to Patala during his incarnation as Vamana. Maha Bali was a great and a favorite devotee of Lord Vishnu. The Lord has granted a boon that Bali will be the next - that is, the eighth Indra (King of Devas) during the time of the eighth Manu, Savarni Manu. Till that time, the Lord Himself decided to protect him in person. The Lord transformed himself into Bali's doorkeeper!
Goddess Lakshmi wanted her husband back in Vaikuntha. She disguised herself as a brahmin woman and went to Patala. She informed King Bali that her husband is away, she has no relatives there and she needs shelter. The generous king offered her shelter and treated her as his sister. He noticed that after the arrival of the brahmin lady his prosperity has multiplied many times.
One day, during the purnima festivals, the brahmin lady tied a knot around the king's wrist with a colored piece of cotton and prayed for the protection of the king. King Bali was touched and asked her to make a wish. She asked the king to send her husband back with her to their home. Perplexed, King Bali asked how he can make this happen. Goddess Lakshmi and Maha Vishnu revealed their original divine form to the king. The virtuous king's joy knew no bounds to see his Lord's love towards his devotees and willingness to forsake Vaikuntha and even Goddess Lakshmi for their sake.
Maha Bali requested Lord Vishnu to return to Vaikuntha with Goddess Lakshmi. But every year Lord spends about 4 months of the monsoon season in the Patala with Bali, from Vaikuntha Ekadashi to Prabodhini Ekadashi.