A certain class of j\xf6tnar are the fire j\xf6tnar, said to reside in Muspelheim, the world of heat and fire, ruled by the fire j\xf6tunn Surtr ("the black one"). The main role of the fire j\xf6tnar in Norse mythology is to wreak the final destruction of the world by setting fire to the world at the end of Ragnar\xf6k, when the j\xf6tnar of Jotunheim and the forces of Hel shall launch an attack on the gods, and kill all but a few of them.