The Deadly Three were three ghosts that entered the world through one of Egon's inventions.
During an incident that led to the creation of the Giant Imp Monster, the power to the Firehouse was severed. While back up power activated, a temp secretary named Louise hid near Egon's invention, a dimensional gate. She mistook the gate's switches as ones for the lights and activated it. The Deadly Three crossed over and manifested.
They got their hands on a Proton Pack and started wrecking up the place. Janine Melnitz managed to save the day when she found another Proton Pack with a reversed stream and used it to cancel the stream fired by the ghosts. Shocked by this occurrence, the three ghosts surrendered. It is unknown what happened to them, but it is likely that the ghosts were put into the Containment Unit. When the Ghostbusters returned from capturing the Giant Imp Monster and saw that the Firehouse was a mess, Janine and Louise left them to clean the mess up.
When two teams of Ghostbusters captured Proteus in their Proton Streams, the god was forced to show them the future. Since eight men captured him at once, he had to show eight futures at once. One of the futures gleaned was of the Deadly Three after they stole a Proton Pack.
- On the subscription cover of Ghostbusters Volume 2 Issue #13, the Deadly Three makes a non-canon cameo.
- Ghostbusters Get Real