Gus is a ghost from The Real Ghostbusters Magazine Summer 1989 story "Did You Call The Plumber?"
After overhearing the Ghostbusters dripping faucet problem, Gus used this as a chance to free the ghosts in the containment unit. Acting as a plumber, Gus managed to fool the Ghostbusters and made his way to his goal. The Ghostbusters soon realized, however, that no one called a plumber and found out that Gus was a ghost. He was soon caught in a trap and transferred into the containment unit, along with the ghosts he intended to free.