According to ancient tradition, there are two main classifications of demons that sexually molest humans—the incubi that assault women and the succubi that seduce men. Both sexual predators are said to have been born as a result of Adam's sexual intercourse with Lilith, a beautiful demonic entity, often said to have been his first wife, or in other traditions, a fantasy wife created to alleviate his loneliness before the advent of Eve. The incubi were said to seduce unsuspecting women by appearing to them in the guise of their husbands or lovers, and as one might suspect, the incubi played an important role in the history of the Inquisition. Even pious nuns appeared before the tribunals, attesting to their affliction by persistent incubi that tried to persuade them to break their vows of chastity. Epidemics of demon possession and erotomania swept such convents as Loudon, Louviers, Auxonne, and Aixen-Provence.
In his book Eros and Evil, R. E. L. Masters remarked on the scant amount of records from the Inquisition concerning the experiences of men who succumbed to seductive succubi in contrast to the enormous number of recorded instances in which women yielded to the sexual attentions of the incubi. Such lack of reports did not imply that succubi were less seductive than incubi, but rested on the belief of the inquisitors and clergy of the day that women were "naturally inclined to vice…and would always put up defenses more feeble than those offered by males."
The incubus could prove to be a jealous lover. In April 1533, according to old church records, an incubus became enraged when he discovered his human mistress in the arms of the son of the tavernkeeper at Schilttach, near Freiburg. In his furious state of mind, the incubus not only set the tavern ablaze, but he burned the entire village to the ground.
Church authorities dealt with the problem of how a spirit could develop a corporeal body by advancing such theories as these: incubi fashion temporary bodies out of water vapor or gases; they have no actual physical bodies, but they possess the power to create an illusion of corporeality; they inhabit recently deceased corpses and animate them for the purpose of sexual intercourse with the living; they actually have material bodies that they can manipulate into any shape they desire.
Father Montague Summers theorized that such demons as the incubi might be composed of that same substance known as ectoplasm from which the spirits of the dead draw their temporary body during materialization seances with mediums. He reasoned that such psychic drainage could occur if a frustrated young person encouraged the attentions of an evil entity by fantasizing about erotic materials.