Dr. Rabbit was born to Bugs Bunny and Mrs. Bunny in 1946. He was raised in a hole where the rabbits lived. He was taught to hate ducks, and hunters everywhere. He lived by these principles until he realized he didn't care about them. Then, he told Bugs to get lost, and went off to find a new home.
He decided to kick down the door of the first building he saw. This plan was generated after three years of thinking. He ran at a door, and broke it down. Colgate was having a conference there, and they decided they liked Dr. Rabbit. They offered him an internship, and he accepted.
In actuality, he only accepted because he had a sudden desire to attack children, and working with Colgate got him just this. He started going on their commercials. He told them "Colgate rules! Now come to..." and he told them his current address (we're not telling you the address for security reasons). When kids came, he killed (and sometimes ate) them. He was sued by Edgar Schneider for child abuse. Dr. Rabbit then fled the country for Rio de Janeiro, and the charges were dropped. However, while in Rio, Dr. Rabbit had a near death experience with Chaz, who attempted to murder him. Luckily, he was able to escape.
When he returned, Colgate eventually fired him, so he went off breaking down more doors, and ripping the children to shreds. The Police went after him, so he went to college, and became a doctor. This is when they started calling him Dr. Rabbit. He then told them he was "Dr. Rabbit", not "Mr. Rabbit", and they went off to find Mr. Rabbit.
Dr. Rabbit was a Psychiatrist/Addiction Specialist for a brief amount of time. In that time, he cured Stu Pickles and Chaz, temporarily. After learning that they reverted back to insanity, he gave up this profession.
Today, Dr. Rabbit lives on Easter Island with his father. He is currently going under an intense therapy treatment to treat his addiction to killing and eating children. It is not successful however, as he still hides in playgrounds, schools, and other places you would expect to see children. He just sits there, and waits... He waits for all of the stupid little fat kids to come by, so he can snatch them away, never to be seen again.