Kubera was the eldest son of the sage Vishrava. Vishrava had two wives. The fist wife give birth to Kubera. The second wife was a rakshasa (demon) woman and gave birth to Ravana, Kumbhakarna and Vibhishana. Kubera used to rule in Lanka and his relations with his cousins were extremely good. But Ravana’s mother did not like idea of her sons mixing so much with Kubera.
She called her sons and said, “What are you up to? Why do you cause me so much of pain? You are demons and Kubera is a god. Is it proper that you should be so friendly with him? The relation between gods and demons is one of enmity. Consider Kubera’s pomp and glory. Have you got anything like that to show for yourselves? Do something so as to improve your own statures.”
Thus instructed by their mother, Ravana, Kumbhakarna and Vibhishana went off to the forest to perform tapasya. They pleased Brahma with their prayers and desired the boon that they might win over the kingdom of Lanka. Ravana also obtained the boon that he would become very strong.
Thus fortified with the boons, the demons attacked Kubera and defeated him. They drove Kubera out of Lanka. Kubera possessed a beautiful Vimana named pushpaka. This was also appropriated by Ravana. Ravana also made it known that whoever gave Kubera refuge would be killed by him. This meant that no one dared give refuge to Kubera.
Kubera sought the advice of his grandfather Pulastya. Pulastya told him to go to the banks of the Goutami Ganga and pray to Shiva there. Shiva appeared before Kubera and blessed him with the boon that Kubera would become the god of all wealth.