Ellis Johnson was a man who worked at the Choate Chemical Plant. After the chemical HOS92 caused Swamp Monsters to attack Dr. Diablo and steal more HOS92, he called the Ghostbusters to help out. After wrapping up the case, the Ghostbusters threatened to charge him if he and Dr. Diablo did not get rid of their toxic products properly.
He first and foremost is a business man. He is concerned only with the bottom line.