The Swamp Monster was created when the Choate Chemical Plant dumped its new chemical HOS92 into the swamp. When it arose, the Swamp Creature wanted the monster to get more of the HOS92. It attacked Dr. Diablo and obtained more HOS92, causing more Swamp Monsters to be created. Ellis Johnson called the Ghostbusters, but Dr. Diablo wanted to solve the problem himself, so he dumped a new chemical called GJMT into the swamp hoping that it would destroy the swamp beings. Instead, it created new purple swamp monsters. The green swamp monsters and the purple swamp monsters then started fighting until the Swamp Creature revealed itself. The Creature explained that the monsters were different bodies for him and then had the monsters get the remaining barrels of HOS92. Dr. Diablo tried to get rid of the creatures again, only to discover that they have already left.
Swamp Monsters are strong and possess regeneration powers. They can also gain intelligence by absorbing people.