Dr. Edam Cheese was doing research into the Lunar Longhorn - a kind of cheese found by astronauts on a visit to the moon. One night when Chester Cheese returned home, he found his father had been murdered. All Chester could find to eat was the Lunar longhorn cheese. This affected him by giving him the ability to shrink in size and he went on to become - Little Cheese, the micro mouse. After helping Captain Carrot and his amazing Zoo Crew, Little Cheese was made a member of the team. He was the only member of the Zoo Crew with powers that didn't originate from an interaction with kryptonite.
He was killed by Feline Faust. But Faust publicly did the murder while disguised as Alley-Kat-Abra, effective carrying out a character assassination of the feline sorceress at the same time.