Dr. Crawler is a were-snake. Originally a scientist with his Uncle Jerry, he wanted a cure for snake venom. He and Jerry injected themselves too soon, along with all the workers and they all became poisonous snakes like rattlesnakes, copperhead, cottonmouth, etc. Ever since, they ran a camp called Camp Hither. Anybody who came was kidnapped and chosen to do tests on and they eventually became snakes too. They start children off like this: Spray them with a sunscreen called Sun-Glo which is actually snake DNA. Then they captured the children and inserted them into weird machines. The machines' laser counter the snake DNA and transform them into snakes on. When they change the child to a full human- not a were-snake, they figure out how to change themselves back to humans. It never worked.
Dr. Crawler was defeated in the ninth book, Welcome to Camp Slither, by Boone and Heather Dixon by accidentally poisoning himself. In the twelfth book, The Streets of Panic Park, Boone and 15 other children found out he is alive with other HorrorLand villains. He made a rare appearance, and when he did he was wrapped around the lab coat of a villain named Inspector Cranium. Both of them along with five other villains helped the Very Special Guests escape Panic Park.