The Swamp Creature was a being that lied dormant in the swamp for eons until it was awakened by HOS92, a product of Choate Chemical Plant. It created an army of Swamp Monsters to get more of the HOS92. This caused so much trouble for Dr. Diablo that Ellis Johnson called the Ghostbusters. Eventually, the Swamp Creature explained that it only wanted to survive and then left with the remaining barrels of HOS92.
After the events that brought it out, it moved to somewhere in the outerworld. It appeared again to help the Ghostbusters defeat Astorath.
The Swamp Creature serves as a hive mind for the Swamp Monsters and has complete control over them.