The North Side Gang is an alliance of several ghosts of mobsters who oppose Al Capone.
When Capone's mob rivals arrived in the Netherworld, they chose to call a truce and retire from crime to become legitimate businessmen. However, when Capone arrived, he refused to let the others retire. He revived the rivalry from their past lives.  An opportunity arose when the Ghostbusters were brought to the Netherworld by Capone. They extracted them and offered a deal to teleport the Ghostbusters back to the physical plane if Capone was taken care of.  Peter Venkman agreed to the terms but Egon Spengler brought up the immediate problem that their Particle Throwers didn't work. The leader gave them Magic Crystals to work in conjunction with the throwers. Once Capone was trapped, the leader honored the deal and teleported the Ghostbusters and Slimer back to the physical plane.
- ↑ North Side Gang (2009). The Real Ghostbusters - "The Ghostbusters Live! from Al Capone's Tomb!" (1989) (DVD ts. 15:32-15:45). Time Life Entertainment. Leader says: "When me and the boys got here, we'd figure we call a truce but Capone, he decides to take over the whole joint. We don't want that. We just want to retire and be legitimate businessmen."
- ↑ North Side Gang (2009). The Real Ghostbusters - "The Ghostbusters Live! from Al Capone's Tomb!" (1989) (DVD ts. 15:19-15:26). Time Life Entertainment. Leader says: "Me and my boys here will help you get back to the world of the living if you help us get rid of Capone."