When and why did India change the name of Bombay to "Mumbai"?

Officially, in 1995. That year, the right-wing Hindu nationalist party Shiv Sena won elections in the state of Maharashtra and presided over a coalition that took control of the state assembly. After the election, the party announced that the port city had been renamed after the Hindu goddess Mumbadevi, the city's patron deity. Federal agencies, local businesses, and newspapers were ordered to adopt the change.