An incubus (plural incubi) is a demon in male form supposed to lie upon sleepers, especially women, in order to have sexual intercourse with them, according to a number of mythological and legendary traditions. Its female counterpart is the succubus. An incubus may pursue sexual relations with a woman in order to father a child, as in the legend of Merlin. Some sources indicate that it may be identified by its unnaturally cold penis. Religious tradition holds that repeated intercourse with an incubus or succubus may result in the deterioration of health, or even death.