> How, when, and why did Bombay become Mumbai?
I did a google on Mumbai and quickly came up with this:
http://theory.tifr.res.in/bombay/
By any other name
The city was called Bombay for much of the last four hundred years. The origin of the name is obscure, but is often said to come from the Portuguese phrase "bom bahia" meaning "good bay". The name Mumbai has been used in the main local languages for as long, and is ascribed to the local goddess, Mumba (ai means mother in Marathi). The name of the city was changed to Mumbai by an act of the parliament in 1997.
I'm just guessing, but I imagine the name change was motivated by increased Indian nationalism under the Bharatiya Janata Party. It appears to be a rejection of a colonial past.
-- John