Bio: A "reptile boy" from a Victorian-era freak show who is befriended by the Seventh Doctor.
In truth, Caval is an alien of undefined origin who befriended the Klathi at some point and began to work for them. Assisted by his Klathi-made robot, Batella, Caval used the cover of the "freak show" to patrol the streets of Victorian London without garnering too much notice. He was principally searching for parts and equipment that could be used by the Klathi to repair their downed space ship.
When Caval discovers that the Klathi will launch their spaceship, even though the power source will destroy all of London, he turns on his former friends and orders Batella to destroy the Klathi vessel.
This act leaves Caval very much alone on 19th-century Earth, doomed to call the freak show his now-permanent home.