Whitey is the Toad's left-hand man, Spike's partner and the (former) surpporting antagonist of the movie Flushed Away.
Background
Its revealed that before becoming a villain, Whitey used to be a lab rat at one of London's biggest laboratories. However, a laboratory accident lead to the destruction of the lab and Whitey was therefor released into the wild and later ended up as Toad's left-hand man.