Incubus creatures are ancient in religion, history, and fiction. The earliest stories of an incubus is from Mesopotamia, where Gilgamesh’s father listed the creature as Lilu. A Lilu disturbed the sleep of women and seduced them.
An incubus is a male demon who lies on women sleepers in order to have sex with them. Incubus try to seduce women in order to father children. If a child is produced it’s called a cambion; it appears to be stillborn, as there isn’t a pulse or visible breathing. Around the age of 7, the child starts to behave like a human child, but it often displays evil tendencies. The child is beautiful, intelligent, and very persuasive.
Unlike a typical vampire, an incubus doesn’t drain its victims of blood or energy, but exhausts them to death with intercourse. The victims become worn out and helpless and often die of asphyxiation.
Mark Beré Peterson: The Haunted South - Hauntings, Urban Legends, History, Folklore and Southern Witchcraft 