Dr. Murkin is introduced as Larry Boyd's doctor. He administers shots for Larry due to issues with his sweat glands. He gives Larry shots every two weeks. Throughout the course of the story, Larry begins to grow hair at a rapid pace, a reaction he originally believes has to do with the expired bottle of Insta-Tan lotion that he and his friends found and used. Soon, Larry's friends begin to disappear one by one. After his body becomes completely covered in hair, Larry rushes home where he is greeted by his parents, who reveal the truth to him.
The town they live in is actually a government testing lab and the adults all work for Dr. Murkin. Years ago, Dr. Murkin created a serum that turns dogs into humans. He used his serum on several dogs, including Larry and his friends. It's why Larry actually needed the shots. It also explains why Larry has no sweat glands. The serum eventually fails and turns the humans back into dogs. Realizing the pain it causes the families who adopted the dog humans, Dr. Murkin gives up experimenting on dogs. However, not long after Larry turns back into a dog, the Boyd family brings home a baby girl named Jasper with yellow cat eyes, alluding to Dr. Murkin having experimented on their cat.
Dr. Murkin is described as being a rather good-natured man who Larry likes, despite constantly giving him shots.
In the book, Dr. Murkin is described as a distinguished-looking man in his fifties with straight white hair that he slicks back, blue eyes and black square-shaped glasses.
- While never given a first name in the book, Dr. Murkin is referred to as Lyle by Larry's parents in the TV episode.