Dr. Diablo was a cruel and careless scientist who was in charge of the Choate Chemical Plant. He created many toxic products and did not care about the harm they did to the environment and his clients. One day, a new chemical he invented called HOS92 was dumped into a swamp and caused Swamp Monsters to infiltrate Choate Chemicals and steal more of the HOS92. Ellis Johnson called the Ghostbusters to take care of the problem, but Dr. Diablo did not want them to get involved because he felt that the Ghostbusters would rat on his operations to the government. In an attempt to solve the problem by himself, he dumped a new chemical called GJMT, but this only succeeded in creating new Swamp Monsters that were purple rather than green and were far meaner. After the Swamp Creature revealed itself, the monsters carried away the remaining barrels of HOS92. Dr. Diablo then plotted to destroy the monsters with a chemical he ordered from another plant, only to discover that the monsters were gone.
Dr. Diablo is a very mean and careless man. He also doesn't seem to think that he will be punished for his misdeeds since he stated that he didn't believe in twist of fate or poetic justice when he is attacked by the Swamp Monsters.