Their bodies were found by Professor Hackle's robot servants and their minds were placed into the brains of robots. Mac was supposed to be a robot-chauffeur (though ironically, he was a poor driver) and Molly was to be a robot-maid, but instead they remained criminals. They first appeared in "The Metallikats" where they kill Katscratch and injure the rest of his gang.
They had a vendetta against Mayor Manx for denying their parole request, though it turned out that Callie had done it as the mayor was too busy to handle it.
Mac and Molly often bickered with each other, but would come to each other's aid when one was in trouble, and it is shown that they truly care for each other. Mac was considered the "muscle" of the team, while Molly was considered the "brains."
In "Metal Urgency," they both discovered the secret identities of the SWAT Kats. However, this knowledge was erased when Commander Feral deactivated them in the same episode as Commander Feral quotes "I don't deal with scum" when they offered to reveal the SWAT Kats' identities to him.
In "Katastrophe," their remains were salvaged by the Creeplings when Dark Kat collaborated with Dr. Viper in a plot to eliminate the SWAT Kats. Dark Kat had special collars placed on the Metallikats' necks which gave them a shock when they didn't do what Dark Kat said. They were sent to capture Mayor Manx and Callie Briggs which was a success. This ended up drawing the SWAT Kats and Commander Feral to the villains' hideout at an abandoned offshore cannery. When the Metallikats turned against Dark Kat, he discovered that Dr. Viper deactivated the collars. In a battle between the villains, Commander Feral, and the SWAT Kats, the villains were defeated and were thought to have been destroyed.
In "A Bright and Shiny Future," the SWAT Kats follow the Pastmaster into a future where Pastmaster had reassembled the Metallikats and had taken over the robots. The Metallikats turn on the Pastmaster and steal his watch. With help from Commander Feral, Felina Feral, Professor Hackle, and the Pastmaster, the SWAT Kats defeated the Metallikats as the Pastmaster reclaims his watch, and in the end, erased this possible future. In some ways they are quite similar to the Superman villain Metallo.