An incubus is a demon in male form who, according to mythological and legendary traditions, lies upon sleepers, especially women, in order to engage in sexual activity with them. 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. Religious tradition holds that repeated sexual activity with an incubus or succubus may result in the deterioration of health, or even death.