The word incubus is derived from Late Latin incubo (a nightmare induced by such a demon); from incub(āre) (to lie upon).[3] One of the earliest mentions of an incubus comes from Mesopotamia on the Sumerian King List, ca. 2400 BC, where the hero Gilgamesh's father is listed as Lilu.[4] It is said that Lilu disturbs and seduces women in their sleep, while Lilitu, a female demon, appears to men in their erotic dreams.[5] Two other corresponding demons appear as well: Ardat lili, who visits men by night and begets ghostly children from them, and Irdu lili, who is known as a male counterpart to Ardat lili and visits women by night and begets from them. These demons were originally storm demons, but they eventually became regarded as night demons because of mistaken etymology.[6]