Dr. Lionel Budgie is a veterinarian that first appeared in the episode Lisa the Veterinarian.
History
When Lisa managed to save a raccoon by performing a CPR, she decided to work at Budgie's office as an intern, but she was so busy taking care of the animals that she forgot to take care of Nibbles, the class pet. He and Lisa tried to do surgery on the hamster, but it was too late and he passed away, making Lisa very sad.
Appearances
Episode – "Lisa the Veterinarian" 
Episode – "Pork and Burns" - Episode – "Dogtown"