Queen Callista is the ancestor of Callie Briggs. The Pastmaster has very strong feelings for her, and wants to make her his queen so he can rule Megalith City with her at his side. However, she repeatedly rejects his "proposals" of marriage and flat-out refuses to become his queen. Callista possesses a magic amulet that allows her to cast spells. She was attracted to Razor when the SWAT Kats came back in time due to the Pastmaster's time vortex.
In Medieval times, Megakat City was known as Megalith City and it was ruled by Queen Callista, assumed ancestor of modern-day Deputy Mayor Callie Briggs. Queen Callista was the target of the unwanted affections of the Pastmaster, who led a magical siege against the city in an attempt to force the Queen to marry him and become his consort. Through the use of an an amulet she wore on a chain, Callista herself was a magic wielder, but her abilities were not as advanced as the Pastmaster’s.
For reasons unknown, the SWAT Kats were brought back to the Dark Ages by a time vortex, and encountered the Queen and her guards. At first thinking them enemies, Callista had her guards attack, until Razor withdrew the Dragon Sword from the stone, signifying him as the hero that would defeat the Pastmaster. This also earned Razor Callista’s affections, much to the chagrin of T-Bone.
Callista was later abducted by the Pastmaster, who used a small army of Cyclops monsters to attempt to level Megalith city. In exchange for the safety of the city, Callista agreed to marry the Pastmaster, but quickly withdrew the offer when the SWAT Kats bested the Pastmaster’s forces. As the Pastmaster attempted to escape with his captive aboard a dragon, the SWAT Kats intercepted (ironically with T-Bone making the day-saving shot using a missile with the Dragon Sword attached to it).
Queen Callista was able to use her magical abilities to send The SWAT Kats back to their own time, but not before recognizing the heroism of Razor with a respective kiss on the cheek.
Queen Callista was seen again in a flashback in The Deadly Pyramid, in a scene that used new footage with Season 2 style animation. Of note, this scene violates the continuity of Bride of the Pastmaster, showing the wedding ring as gold instead of silver, and the amulet (which had been destroyed earlier in the episode) still intact around her neck.