Kubera, son of Rushi Vishrva performed hardest of all tapasyas and as a result Lord Shiva blessed him to be Lokpal, guardian of all the wealth of the world and equal of the gods Yama, Indra & Varuna. Lord Brahma (his great-grand-father) gifted him Pushpak viman as well.
Being the eldest of all brothers, Kuber used to rule the kingdom of Lanka. Ravana, his half-brother also worshipped Lord Shiva and acquired unbeatable power as blessings from him. After acquiring all the powers, Ravana asked Kubera to return the regime of Lanka to his daitya dynasty. As per the advise from his father Rushi Vishrva, Kuber gives away the kingdom of Lanka to Ravana and builds a beautiful kingdom of Alkapuri in Himalayas which was full of breathtaking gardens and lakes and more. It was even envied by Devas of the dev lok. Kubera continued his reign as Lokpal from Alkapuri and kept traveling around the world in his Pushpak viman. But this did not last long. Envied by richness of Kubera, Ravana attacked him once again. Yaksha army of Kubera fought the battle with great bravery but the Daitya army of Ravana was more than a match for them which defeated them. He drove Kubera out of Lanka. Ravana even took away Pushpak viman from Kubera. Once again defeated Kubera pleases the Lord Shiva with his tapasya. Lord Shiva asks him to worship him by setting up a shiv mandir and please goddess Amba to be there at the same temple to protect him from Ravana & other evils of the world.
That is the Kubereshwar Mahadev temple, located on the bank of holy river Narmada, near Chandod, in the district of Vadodara.