Lionel Watson is a resident of Teras Terrace who thrives on high temperatures, and makes his home in a specially constructed artificial volcano. Though he generates enough internal heat of his own to stand cooler temperatures for short periods, after a while he becomes very uncomfortable, and left for too long without enough heat he stiffens into immobility. When he must go out for hours at a time, he brings along a tank of lava he can spray himself with to keep warm.
Of course, the inconvenience to Lionel of having to keep warm goes both ways: it's rather uncomfortable (to say the least) for others around him not inured to high temperatures. If proper precautions aren't taken, cloth and carpet and other flammables catch fire in Lionel's presence. Still, he can occasionally make himself useful; sometimes when high temperatures are needed Lionel can provide them more cheaply than they can be arranged otherwise.