The festival of Onam in south India begins on September 6 and end on September 15.
It is in honor of an ancient Indian ruler named Mahabali who was known for his generosity and virtuous conduct.
Due to the large spiritual merit attained by him in this universal cycle, Mahabali is said to ascend to the post of Indra, the king of the gods in heaven, in the next universal cycle.
https://en.wikipedia.org/wiki/Onam