When Shigeru Miyamoto and his team were working on Super Mario 64 for the Nintendo 64 one of the first things they created was a blank, featureless level in which Mario had to chase and capture a yellow rabbit. This level was used to test the 3D Mario model and to work out the controls for the upcoming game. Like Miyamoto's Penguin, the little rabbit struck a chord with the development team and they decided to place him in the finished game. Down in the castle basement Mario encounters the rabbit where he must chase and capture him. Doing so will earn Mario a star. The rabbit's name? Mips, after the CPU chip.

In 2004 Nintendo upgraded Super Mario 64 for the Nintendo DS handheld system. In the new Super Mario 64 DS Mips returns with a cadre of rabbit brothers who give up keys to unlock mini-games when caught. These new rabbits are multicolored, but all of them are based on the original Mips design.


References:
Super Mario 64 Player's Guide
Nintendo Power interview with Shigeru Miyamoto in 1996
http://ds.advancedmn.com