A Mage, in Tholian society, is an individual who can move freely from one caste to another, and is also capable of modifying other individuals to function in new castes. Given the strict division of societal roles in Tholian culture, these individuals play an important role in keeping society in balance.
In 2267, a Mage named Naskeel joined a splinter group of Tholians, calling themselves "the Children of the Lost Ones", who were dubbed "Outsiders" by the Tholian Assembly and decreed to have no role in society. That year, Naskeel was captured by Starfleet personnel at Deep Space Station M-33, and requested political asylum rather than being returned to the Tholian Assembly. With the assistance of Captain James T. Kirk and his crew of the USS Enterprise, Naskeel was saved from extradition back to the Tholians, and began negotiations for how to adapt the Outsiders to serve their society. (TOS short story: "Fracture")