A scientist whose inventions always seem to go wrong. In his first appearance, he was hired by Warden Cyrus Meece of Megakat Maximum Security Prison to invent a gem-mining gadget called the Gemkat 6000, designed to separate rare and precious stones from rock without digging. But when Rex Shard, the prisoner testing the device, tried to steal some gems from the device, an explosion erupted which turned his body into crystal. Dr. Greenbox attempted to rewire his prototype in order to reverse the effect, but he was turned into crystals by Shard, and remained so until the SWAT Kats managed to cure Shard themselves. Later, while working at Megakat University, Dr. Greenbox created an artificially-intelligent device called a Micro-Brain Repair Unit, which, after having its programming contaminated by the Metallikats, evolved into a self-aware mechanical entity called Zed, building a robot body around itself using any metal objects it could get its hands on. Though Dr. Greenbox originally attempted to help the SWAT Kats destroy Zed, once inside his head, he was so overwhelmed at how much his creation had evolved that he turned against them and merged with his machine; after Zed's brain was destroyed, Greenbox collapsed and was turned over to the Enforcers, after which his fate is uncertain.