Bali was a very benevolent king and a devotee of Lord Vishnu. Bali had a hundred sons, of whom Banasura with his thousand arms was the eldest. Banasura was a devotee of Lord Siva, and when Siva performed his famous 'Tandav' dance, Banasura used his thousand arms to play the 'mridanga' in accompaniment. Pleased with his devotion, Lord Shiva asked Banasura to demand a boon. Banasura asked for Siva
to be his protector just like Lord Vishnu was his father's protector. The boon was granted, and Banasura became invincible. Soon he became cruel and arrogant, so much so, even the gods were afraid of him.
Banasura had a pretty daughter by the name of Usha. Many suitors came asking for her hand, but Banasura refused them all and had her shut in a fortress called 'Agnigarh' along with her friends.
In her sleep Usha saw a handsome young man and fell in love with him. Chithralekha was a close friend of Usha and a great artist. She drew a picture of the young man based on Usha's descriptions. When the drawing was completed, they both knew the young man was Anirudh, the grandson of Lord Krishna. Using her magical powers Chithralekha flew to Dwaraka and brought Anirudh to Usha's side, and they lived together. In course of time Banasura learned about this and flew into a rage. He bound Anirudh with snakes and had him imprisoned.
When Lord Krishna heard about this he came with a mighty army to rescue Anirudh. A great battle ensued. Lord Siva joined the fray, fighting on behalf of Banasura. But even after prolonged fighting Lord Siva was not able to defeat Lord Krishna, and eventually sued for peace, begging Lord Krishna to spare the life of his devotee Banasura. Lord Krishna agreed and granted immortality to Banasura, but cut off all but four of his thousand arms. He brought Anirudh and Usha to Dwaraka amidst much rejoicing and jubilation..
Banasura retired into the Himalayas to spend the remainder of his life in the service of Lord Siva