"Radie" was a slang term for human beings who had been mutated by the Sun's radiation in the future. These mutations were hereditary, so even those not directly affected could inherit them from their parents. Radies were relatively commonplace in the 23rd Century, at least in the city of Haddyn. Gunther was an example of a radie, his mutation taking the form of a fish-like physiology which required him to live underwater to survive.