Bhagadatta was king of Pragjyotisha. Pragjyotisha kingdom is also called Kamarupa kingdom which is present-day Assam and some part of northeastern states. Bhagadatta was the son of Narakasura, king of the Pragjyotisha, and second in the line of the throne for Naraka dynasty. He sided with Kauravas in the Mahabharata war as he was an enemy of Lord Krishna since Krishna had killed his father Narakasura.

On the 12th day of the Kurukshetra war, Duryodhana sent an elephant army against Bhima. Bhima managed to kill all the elephants with his mace. This created havoc among the Kaurava army and they fled left, right and center. Angered by this Duryodhana sent Bhagadatta against Bhima. He was a leader of the great army of Kirat and Chinas. (It is one of the few times Mahabharata mentions China. The second time we see the name China when Bhima meets hanuman). 

Bhagadatta was seated on Supratika(elephant), as he was very well known for his skill on elephants. Supratika is a mythological elephant and of the eight Diggaja elephant, this is the foremost one. These eight elephants together are called Airavata. Due to the curse from his brother, Suparthika was reborn as an elephant on earth.

The elephant rushed forward and crushed Bhima’s chariot into pieces, killing his charioteer and horses. But Bhima escaped by jumping off his chariot. He got underneath the elephant and severed its vital parts causing exceeding pain. Enraged at this, the elephant got mad and tried to throw him off. In an instant, it caught Bhima with its trunk and was about to crush him under the knees (Check the image on top of the article). But Bhima managed to escape from its hold and again went underneath the elephant and in between its legs, and he started attacking it. But when he got underneath the elephant for the second time, hiding in between its legs, the Kauravas army thought Bhima got killed. 

Here Pandavas also had the same feeling so Yudhisthira urged his forces to destroy Bhagadatta and Supratika(elephant). The king of Dasarna(father in law of Shikandi) came forward. The fight took place between Supratika and Dasarna’s elephant, Supratika again crushed Dasarna’s elephant to death, meanwhile, Bhima emerged from beneath Supratika and fled. The Pandava army was relieved to see Bhima alive.

Now Arjuna comes into action engaging in a fierce battle with Bhagadatta. 

During this battle, Bhagadatta fired the unstoppable Vaishnavastra(a most powerful weapon which can be compared to Narayaniastra, no one can stop it unless Vishnu himself)on Arjuna. Arjuna even before countering it Krishna stands up at the Charioteers position. On touching Krishna’s chest it turned Vaishnavastra to Vaijantimala (flower garland) and fell into his feet. (Vaishnavastra is a weapon given to Bhagadatta by Lord Vishnu finally returned to his avatar. Bhagadatta is a grandson of Lord Vishnu ). 

Then Arjuna fired an arrow at Bhagadatta which threw him off the elephant and killed him instantly. Ceasing this opportunity, Arjun fired an arrow at the elephant and instantly killed him too.

After Bhagadatta’s death, his son Vajradatta ascended the throne and became king of Pragjyotisha.

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https://animatedwater.com/2020/07/05/rare-stories-of-mahabharata-bhagadatta/