The Space Mice were inside Allura's cryo-pod with her during the 10,000 years she spent in stasis, and she discovered them soon after awakening and was comforted to know that she and Coran were not the last inhabitants of Altea left. Subsequently, she learned that the time she and the mice had spent in the pod together had given them a mental link that allowed them to understand each other, which proved invaluable as the mice were able to crawl into spaces too large for her and Coran to enter in order to make repairs to the Castle of Lions. They demonstrated enough intelligence to understand other beings as well, or else strong powers of observation, as they learned that Pidge was a girl posing as a boy and later conveyed this to Allura. They would later assist Pidge in lowering the castle defenses after Sendak took over, with Allura sending them a telepathic message.
When the castle became trapped in a wormhole loop, it caused the Space Mice to mutate into a variety of different alien animals each time they restarted the loop, similar to how Coran continued to grow younger and younger; they all returned to normal after Pidge sent a signal that allowed Allura to bring the ship out of the wormhole. Platt, another of the mice, later took something of Coran's, prompting the Altean to search for him. The mice would later keep Allura company while the others were away on various missions, performing a circus act, braiding her hair, and playing charades.
- Platt is the largest mouse with yellow and green fur.
- Chulatt is the smallest mouse with blue fur and blue eyes.
- Plachu is the blue mouse with red eyes.
- Chuchule is the pink mouse with red eyes.
- The Space Mice originally appeared in Voltron: Defender of the Universe.