Wikipedia
Rukmi ( Marathi रुक्मी) was the ruler of Vidarbha according to the epic Mahābhārata. He was the son of king Bhishmaka and elder brother of Rukmini. Krishna married Rukmini by abducting her from the Vidarbha kingdom, though Rukmi wanted to give her as bride to Chedi king Shishupala. He fought with Krishna, but was defeated. When Krishna was about to kill him, Rukmini begged that spare her brother's life. Krishna agreed and let Rukmi go free, but not before having his head shaved as a visible sign of a warrior's defeat.
Rukmi never returned to his capital Kundinapuri in Vidarbha. Instead he created another capital called Bhojakata to the west of Kundina and started ruling the country from there.
Rukmi later became friends with Krishna. However Rukmi was not accepted by Arjuna or Duryodhana as an ally in the Kurukshetra War, because of his boastfulness. Thus Rukmi's Vidarbha army stayed away from the Kurukshetra War, becoming a neutral army in the encounter between the Kauravas and the Pandavas.