Story of Rukmi is found in the Mahabharata. Rukmi was the son of Bhishmaka, King of Vidarbha, and brother of Rukmini (wife of Krishna). He performed intense austerities and attained Brahmastra (powerful arrow) from Parashurama and other Divyastras from Sage Druma. However, Rukmi was rude and arrogant and even his father could not control him.
Rukmi wanted Rukmini to marry Shishupala, king of Chedi. But Rukmini was in love with Krishna. Sri Krishna carried her away from temple on the day of her marriage.
Rukmi and his army chased Krishna but were defeated.
Feeling utterly humiliated, Rukmi did not return to Kundinapura, the capital of Vidarbha. He founded a new township named Bhojakata and it later became the capital of Vidarbha.
Rukmi then did intense penance and pleased Shiva who blessed him with Mahendra weapon. With this weapon, he expanded his kingdom.
His relationship with Sri Krishna became cordial in later years. Subhagi, daughter of Rukmi, married Pradyumna, son of Sri Krishna.
Once Balrama, elder brother of Sri Krishna, and Rukmi started playing dice. In one of the stakes, Rukmi lost the game but refused to admit defeat. Enraged at this, Balarama killed Rukmi.