Aniruddha (Sanskrit: अनिरुद्ध), meaning "uncontrolled", "unrestrained" or "without obstacles", was the son of Pradyumna and the grandson of Krishna. He is said to have been very much like his grandfather, to the extent that he may be a jana avatar, avatar of Vishnu. The four important Vishnu extensions are Vasudeva, Sankarsana, Pradyumna, and Aniruddha. These four are considered to be vishnu-tattva or Vishnu's plenary expansions. Aniruddha is present in every soul as Supersoul.
A Daitya princess named Usha, daughter of Bana, fell in love with Aniruddha and had him brought by magic influence to her apartments in her father's city of Sonitpura in Assam. However, according to some legends, Shonitpur is also identified with Sarahan in Shimla district of Himachal Pradesh. Going by their legends, Pradyumna was made the king of Shonitpur & subsequently the Bushahr state by Lord Krishna himself. Bana sent guards to seize him, but the valiant youth, taking an iron club, slew his assailants. Bana then brought his magic powers to bear and secured him.
On discovering that Aniruddha had been carried away, Krishna, Balarama, and Pradyumna went to rescue him. Bansura was a great devotee of the god Shiva and had 1000 arms, as a result of which no one had ever been willing to fight him. Blinded by his pride, he asked Shiva to give him a chance to fight with someone as strong as himself. Shiva therefore cursed him to defeat in war by Krishna, an Avatar of Vishnu.
Only after some months Krishna came to know where his grandson was and launched an attack on Banasura with a big army. Thus a great battle was fought.
When the army laid siege to his city, Banasura staged a fierce counter-attack. At this point, Lord Shiva joined the battle against Krishna because he had promised protection to Banasura. The fight was intense in all directions, and Siva (also known as Mahesvara) caused a mighty fever with three heads and three legs (Mahesvari jvara). But Krishna generated a counter-fever. Ultimately Krishna’s forces were close to victory and Krishna himself was vigorously cutting off the myriad arms of Banasura. Siva again intervened because of his promise to Banasura.
Krishna, however, assured Siva that he had no intention of killing Banasura, but would leave him with only four arms so that his power would be limited. However, in honour of the demon’s boon from Siva, Krishna promised that Banasura would have nothing to fear from anybody in the future.
Gratefully, Banasura prostrated before Krishna and then had Aniruddha and his bride, Usha, brought to Krishna in a regal chariot. All then returned to Dvarka, where Krishna’s victory in the combat with Siva was celebrated with festivity.
Please refer Srimad Bhagvatam chapter for complete sequences of the battle for more factual details.
Two crucial references are present in the Nalayira Divya Prabandham about the episode of how Krishna fights with Banasura. One is in the Tiruvaimozhi of Nammazhwar and another in the iRamanusa Nootrandhadhi. Specifically the pasuram no 8 belonging to the 7th Centum 4th Decad (starts with aazhi-yezha) - "ner sarindhan .... konda-vanre" and the pasuram no 22 of iRamanusa Nootrandhadhi "karthigaiyaanum ... "
Bana was defeated, but his life was spared at the intercession of Shiva, and Aniruddha was carried home to Dwaraka with Usha as his wife. He is also called Jhashanka and Ushapati. He had a son named Vajra, whose lineage is traced to the royal family of Jaisalmer.
- Dowson: Classical Dictionary of Hindu Mythology.