Vajra (king)

According to the Mahabharata and the Puranas, Vajra, (in Sanskrit: वज्र or वज्रा), also known as "Vajranabh" (वज्रनाभ्), was one of the last survivors of the Yadu dynasty. He succeeded his father King Aniruddha to the throne of Mathura. He was the great grandson of Shri Krishna and the grandson of Pradyumna.

Shri Krishna's wife, Rukmini, gave birth to the great warrior Pradyumna, one of Krishna's prominent sons, who later married the daughter of his maternal uncle Rukmi, Rukmavati. The mighty Aniruddha, was born to them, who married Usha, the Daitya princess. The princess gave birth to Vajra, who was known as the invincible warrior and would remain among the few survivors of the Yadus' battle. The name Vajra means "thunderbolt" or "diamond". A Vajra is a virtual object that represents firmness of spirit and spiritual power.

After Krishna left for Vaikunta, about 36 years after the Kurukshetra War (3138 BC), most of the major Yadu leaders had long died either due to disputes among themselves or the submergence of Dwarka into the sea. Arjuna went to Dwarka to bring the last surviving Yadus (i.e. Krishna's great grandson Vajra and the Yadava wives and elderly people) to safety in Hastinapur. Arjuna then proclaimed Vajra as the king of Mathura at Indraprastha.

Just before Pandava left for the Himalayas, Arjuna's grandson Parikshit was crowned the King of Indraprastha by Yudhishthira. King Parikshit went to Mathura to visit King Vajra to inquire about his well-being. Parikshit was welcomed with great respect by Vajra and in return Parikshit expressed his obligation towards Vajra, for his great grandfather Krishna had saved his entire dynasty in war with Kaurava. When asking King Vajra whether he needed any help, the King replied, "Although I am now the King of Mathura, I am unable to enjoy the rule. The happiness of a kingdom is due to the people that live there and I have no idea where the residents of this place have gone. Mathura is deserted." On hearing this, King Parikshit immediately sent out for Sage Ṣāṇdilya, a preceptor to King Nanda, in order to clear Vajra's doubts.

...
Wikipedia