Rex Shard was a convict serving a nine-life sentence at Megakat Maximum Security Prison. Shard was chosen by Warden Cyrus Meece to operate the Gemkat 6000 in its trial run. In return, Meece would shave some time off of Shard's prison sentence. Amazed at how quickly the Gemkat 6000 worked, he attempted to open the drill housing to get at the collected gems within and "take a few off the top." In doing so, he somehow caused the machine to backfire and explode. When Shard emerged from the mine, he found that the explosion had somehow caused him to begin to rapidly change into a being made of unbreakable green crystal.
Shard quickly discovered that he had the ability to turn whatever he touched into crystal, when he seized and crystallized his guards Talon and Lem merely by touch. He then proceeded back to the prison, thirsting for revenge against the ones he deemed responsible for his accident. When he reached the perimeter wall, he put all his energy into turning it to crystal, which then caused him to complete his transformation into a totally crystalline being. Ignoring the fire from the prison guards, he punched through the brittle wall and entered the prison. He burst into Warden Meece's office in the same manner, and turned him to crystal right before the eyes of a terrified Deputy Mayor Callie Briggs and Dr. Greenbox. The latter, who had created the Gemkat 6000, was next on his hit-list.
Before he could even attempt to to harm to the Deputy Mayor and the inventor, the Swat Kats arrived, summoned by distress calls from the prison. He was hit in the chest with a blast from their cement machine gun, and sent flying into the Warden's private diamond vault. This gave Deputy Mayor Briggs and Dr. Greenbox time to slip from the room, but coming into contact with the diamonds somehow caused a reaction in Shard's body. He grew to titanic proportions, bursting through the prison roof. It was here he further explored his amazing powers. The impenetrable crystal shell surrounding his body made any conventional weapons useless against him. The Swat Kats' newly developed Slicer Missiles broke apart when they hit him, for instance.
The lasers of the Enforcer tanks which arrived shortly thereafter bounced harmlessly off him. Shard then found he could form crystal shards in his hands and hurl them as projectiles, or even do the same with his impressive abs. Using this technique he disabled both the Turbokat and Commander Feral's personal tank. But during this battle, his target had managed to escape: Briggs and Greenbox had fled in the Doctor's jeep to Gemkat Labs, after retrieving the Gemkat 6000 from the mines to try and work on a way to reverse Shard's condition. Having a pretty good idea of where Gemkat Labs was, Shard stomped off towards it. This took him through Megakat Springs, where he interrupted the Manx Invitational Golf Tournament.
After fending off more Enforcers, Shard turned the entire golf course and everyone there to crystal, including Mayor Manx, and once again got the best of Feral when he disabled the Commander's chopper. He then headed to Gemkat Labs, where he stopped Greenbox from finishing rewiring the Gemkat 6000 by grabbing and crystallizing him at last. The Deputy Mayor was his next target, but T-Bone suddenly came out of nowhere (at least as far as Shard was concerned) on the Sandkat and whisked her to safety, the Gemkat 6000 with her. Shard tried to stop them by touching the ground and sending a "wave" of crystal after them, but the Sandkat leapt over a canyon to safety.
Undeterred and now mad with power, Shard head for Megakat Dam, turning random landforms to crystal as he went. Meanwhile the Swat Kats had finished what Greenbox had started and rewired the device. They came after Shard, who had succeeded in turning the reservoir to crystal, and a fierce battle ensued over the frozen expanse of the crystallized water. The Gemkat 6000's beam was unable to penetrate Shard's armor, and Banshee Missiles barely made even tiny cracks in him. Annoyed at the "Swat Gnats," Shard suddenly came up with a brand new power. He focused the sun's rays through his crystal hand into a deadly heat beam, which he used to shoot down the Kat's Eye News chopper when it became annoying to him as well.
The Turbokat proved too difficult for him to hit, and right at that moment T-Bone came up with an idea to defeat Shard. A Mach 5 sonic boom as the jet flew past Shard at an alarming speed rocked the crystal giant and with an agonized scream, he broke apart, turning back into a normal sized, and unconscious, crystal cat. The vigilantes then used the Gemkat 6,000 to return him fully back to normal. As a result, everything he had turned to crystal also returned to its normal state. Shard was then taken into custody by the Enforcers and returned to prison.
- Rex Shard was slated to make a second appearance, in an episode entitled Cold War. He would have gained power over the weather by diving into an experimental energy source at the Megatech Power Station, which transformed him into a walking heat sink. Absorbing all of the heat around himself, he was to have frozen the city. Eventually, the SWAT Kats would've defeated him using a Lava-Missile, which caused him to absorb more heat than he could stand. He threw himself off of a cliff, shattering thousands of feet below, and as before his defeat caused everything to return to normal, including himself. As he was arrested, he would've vowed to return. However, Cold War was never produced, existing solely as a story treatment by Lance Falk.
- Swat Kats: "Chaos in Crystal" (1993)