The Incubus is the male sex-demon of medieval European demonology: a fiend that comes to women in the night, lying upon and pressing the sleeper as it forces itself upon her in her sleep, draining her vitality and sometimes begetting monstrous or uncanny offspring — the male counterpart of the [succubus], and a being bound up with the night-terror, the nightmare, and the dread of demonic assault. It is the night-lying demon, the male assaulter of sleepers.
The Demon That Lies Upon
The Incubus (from Latin incubo, “to lie upon”) is the male sexual demon of Christian and medieval European demonology — a fiend that visits sleeping women by night and lies upon them, pressing them down (the word is kin to the “nightmare” that presses the chest, and to the German [alp]) and forcing sexual congress upon them in their sleep. The experience it embodied — the sense of a heavy, suffocating presence in the night, paralysis, and erotic or terrifying dreams — is that of sleep paralysis and the nightmare, given the form of a lustful demon.
The Assault and the Offspring
The incubus was held to drain the strength, health, and even the life of its victims through its repeated nightly assaults, leaving them weakened, sickly, and tormented. More dreadful still, medieval theology held that an incubus could beget children upon the women it assaulted — producing offspring that were uncanny, deformed, or monstrous, or in some accounts simply human but demon-fathered (the wizard Merlin was said to be the son of an incubus). The elaborate demonology of the witch-hunting era (the Malleus Maleficarum and its kin) treated incubi and succubi at length, and explained that the same demon might act as a [succubus] to take seed from a man and then as an incubus to deliver it to a woman.
The Demon and the Nightmare
The incubus belongs to a vast, cross-cultural family of night-demons and nightmare-spirits that assault sleepers — the [alp] and [drude] of Germanic lore, the mare, and the sexual night-demons of many traditions — the supernatural explanation for sleep paralysis, erotic dreams, nocturnal terror, and unexplained illness or pregnancy. In the witch-trials it was a grave and literal danger, and accusations of congress with incubi were part of the machinery of persecution. From medieval demonology the incubus has passed into modern horror and fantasy as the archetypal lustful male demon. In the Incubus, medieval Europe gave form to the night-lying demon — the male fiend that presses upon and assaults sleeping women, draining their life and begetting monstrous offspring, the demonic face of the nightmare and counterpart of the succubus.