Diwali as Balirajya In Kerala
In Kerala, the festival of light used to be celebrated a night after Diwali to mark the return of a benevolent demon king Mahabali to the earth. It is now celebrated as a 10 day Onam festival.
According to Bhavishyottara Purana and Brahma Vaivarta Purana, king Mahabali was banished to depths by the Vamana incarnation of Lord Vishnu. Medieval author Al-Biruni has given a detailed account of rituals, practices and tradition of Indian people.