To Sumerians, Babylonians, Assyrians, and Jews there were male and female demons (Jewish demons were mostly male, although female examples such as Lilith exist). In Christian demonology and theology there is debate over the gender and sexual proclivities of demons.
Traditional demons of Christianity, such as Satan, Beelzebub, and Asmodeus are almost invariably assigned a male gender in religious and occultist texts. This is true also for succubi, who despite taking a female shape to copulate with men, are often thought of as male nonetheless.
The Testament of Solomon, an early treatise on demons of Judeo-Christian origin, presents the demon Ornias, who assumes the shape of a woman to copulate with men (though in other versions he does it while in the shape of an old man). After meeting him, king Solomon asks Beelzebub if there are female demons, suggesting a difference between male shapeshifting demons (incubi/succubi) and genuine female demons. Similarly, angels in Christianity have also masculine genders, names and functions. For example, the Grigori, led by Azazel, descended on Mount Hermon and copulated with earthly women out of lust, having children with them.
John Milton in Paradise Lost, specifies that although demons may seem masculine or feminine, spirits "Can either Sex assume, or both; so soft And uncompounded is thir Essence pure". Nonetheless, these feminine shapes may be just temporal disguises to deceive people, just as at one point Satan takes the shape of a toad. Everywhere else demons are described as male, and Satan is the father of Death with Sin, a female spirit. In Paradise Lost, Adam explicitly states that all angels of heaven are masculine:
"Oh, why did God,
Creator wise, that peopled highest Heaven
With Spirits masculine, create at last
This novelty on earth, this fair defect
Of Nature, and not fill the world at once
With men as Angels, without feminine?"
Demons may be considered androgynous, but the general view is that they are masculine and feminine, while not actually being of either sex. This is the general view of the angels as well, who are generally considered sexless.
Gregory of Nyssa (4th century), as well as Ludovico Maria Sinistrari (17th century), believed in male and female demons, or at the very least demons having male and female characteristics.
Lust in demons is a controversial theme for Christian demonology, and scholars disagree on the subject.
Augustine of Hippo (5th century), Hincmar (early French theologian, archbishop of Rheims, 9th century), Michael Psellus (11th century), William of Auvergne, Bishop of Paris (13th century), Johannes Tauler (14th century), and Ludovico Maria Sinistrari (17th century), among others, supported the idea that demons were lustful and lascivious beings.
Plutarch (1st and 2nd centuries), Thomas Aquinas (13th century), Nicholas Remy (16th century), and Henri Boguet (16th and 17th centuries), among others, disagreed, saying that demons did not know lust or desire and cannot have good feelings like love; as jealousy would be a consequence of love, they could not be jealous. Ambrogio de Vignati agreed with them.
Heinrich Kramer and Jacob Sprenger (15th century), authors of the Malleus Maleficarum, adopted an intermediate position. According to their book, demons did not feel love for witches. This is because sexual relationships with them were a part of the diabolical pact these men and women made with Satan. Demons acting as incubi and succubi with common people were passionate lovers that felt the desire of being with their beloved person and have sexual intercourse with him/her.
Augustine, Hincmar and Psellos thought that lust was what led demons to have sexual relationships with humans. William of Auvergne conceived the idea that demons felt a particular and morbid attraction to long and beautiful female hair, and thus women had to follow the Christian use of covering it to avoid exciting desire in them. Tauler had the opinion that demons were lascivious and thus they wanted to have sexual intercourse with humans to satisfy their lewdness. Sinistrari supported the idea that demons felt sexual desire, but satisfaction and pleasure were not the only motivation to have sexual relationships with humans, another reason being that of impregnating women.
Plutarch wrote that demons could not feel sexual desire because they did not need to procreate; his work inspiring later Remy's opinion. Thomas Aquinas asserted that demons could not experience voluptuousness or desire, and they only wanted to seduce humans with the purpose of inducing them to commit terrible sexual sins. Remy wrote that "demons do not feel sexual desire inspired by beauty, because they do not need it to procreate, having been created since the beginning in a predetermined number". Boguet said that demons did not know lust or voluptuousness "because they are immortal and do not need to have descendants, and so they also do not need to have sexual organs", so demons could make people imagine that they were having sexual relationships, but that actually did not occur. Vignati agreed with Boguet saying that sexual relationships with demons were imaginary, a mere hallucination provoked by them, and Johann Meyfarth agreed too.
By supporting the idea that demons could rape women and sexual relationships with them were painful, Nicholas Remy assigned a sadistic tendency to their sexuality.
Pierre de Rostegny supported the idea that Satan preferred to have sexual intercourse with married women to add adultery to other sins like lust, but told nothing about his lust or that of other demons.
Supporting the idea that demons had feelings of love and hate, and were voluptuous, there are several stories about their jealousy.
The first story of this type is narrated in the deuterocanonical Book of Tobit, in which the demon Asmodeus either fell in love with Sarah or felt sexual desire for her (or both). Out of jealousy, Asmodeus killed seven of her husbands before the marriages could be consummated. Asmodeus never had sexual intercourse with Sarah, and intended to kill Tobias, her eighth husband, but was foiled by the angel Raphael.
Another of these stories about demonic lewdness and passionate love is told in The Life of Saint Bernard, written by a monk, and said that during the 11th century a demon fell in love with a woman, and when her husband was asleep he visited her, awoke the woman and began to do with her as if he were her husband, committing every type of voluptuous acts during several years, and inflaming her passion.
A story referring to demonic jealousy was told by Erasmus (16th century), who blamed a demon for the fire that destroyed a village in Germany in 1533, saying that a demon loved deeply a young woman, but discovered that she had also sexual relationships with a man. Full of wrath, the demon started the fire.
Christian demonologists agree that sexual relationships between demons and humans happen, but they disagree on why and how. A common point of view is that demons induce men and women to the sin of lust, and adultery is often considered as an associated sin. Pierre de Rostegny supported the idea that Satan preferred to have sexual intercourse with married women to add adultery to her sins.
Gregory of Nyssa said that demons had children with women called cambions, which added to the children they had between them, contributed to increase the number of demons.
It was considered that demons always had sexual relationships with witches in the form of incubi and succubi, and some witches allegedly had sexual intercourse with the Devil in the form of a male goat. But common people, as it was believed, also were seduced by incubi and succubi, especially while they were asleep, and sometimes when they were awake, in the form of a beautiful man or woman that excited their desire to the point of not being able to resist the temptation, although the possibility of resistance always existed as asserted by Christian theologians, but the tendency to sin was stronger than their faith. Francesco Maria Guazzo offered detailed descriptions of sexual relationships between demons and humans.
Nicholas Remy, disagreeing with many theologians and demonologists, supported the idea that even if a woman opposed resistance to the demon he could rape her, and wrote about a case of a young teenager that "was raped twice the same day by a demon, although she opposed resistance, and, her body not being mature enough to receive a man, she almost died because of the hurts". Catherine Latonia confessed this case to him in 1587. Whether the confession was an excuse to avoid giving the name of the rapist or the girl actually thought that a demon had raped her will remain unknown. Sylvester Prieras agreed with Remy, supporting the idea that demons could not only rape common women but also nuns.
The Malleus Maleficarum established that sexual relationships between demons and humans were an essential belief for Christians. But its authors considered also the possibility that demons provoked a false pregnancy in some women, filling their belly with air due to certain herbs they made them drink in beverages during the Sabbaths; at the time of giving birth to the child, a big quantity of air escaped from the woman's vagina. The false pregnancy was later explained by medicine.
Many Christian theologians (Martin Luther and Jean Bodin among others) believed that demons could impregnate women but their children would have a short life and be good for nothing; other theologians (Francisco Valesio, aka Valesius, Tomaso Malvenda and Johann Cochlaeus among others) thought that these children could be important characters, like Attila, Martin Luther, Melusine or the Antichrist.
Augustine of Hippo, Pope Innocent VIII, Albertus Magnus, Thomas Aquinas, Peter of Paluda, Martin of Arles and Ludovico Maria Sinistrari believed that demons could fecundate women, but Ulrich Molitor, Heinrich Kramer, Jacob Sprenger and Nicholas Remy disagreed.
According to Remy, sexual relationships with demons were painful, meanwhile many persons that confessed to having had those relationships told that they were satisfying.
Henri Boguet and Johann Meyfarth supported the idea that demons provoked an imaginary coitus because they did not have sexual organs, such as a penis or a vagina.
In Genesis chapter 6 the "sons of God", presumed by some to be fallen angels, mate with human women, creating a race of super-beings called the Nephilim.
This interpretation is disputed by some, who claim that "sons of God" in that text refers only to believers in the "Promised Seed" (Genesis 3:15) and that "daughters of men" refers to pagan women, particularly implying that descendants of Seth were marrying descendants of Cain.
Under this interpretation, the Nephilim were not physical giants, but just men without conscience who were extremely malicious and aggressive. This interpretation limits the direct roles of demons on the early human race to merely a role as being influential to human affairs, without actually engaging in sexual relations with humans themselves. Under this, the Nephilim is the offspring of the falling angels but were full-blooded men that were particularly susceptible to demonic influence over their actions.
This argument derives from messianic interpretations of the Old Testament, which hold that humans need deliverance from Yahweh's judgement because of sin, claiming that demons only attempt to stop humans from having faith in a messiah, and can achieve this without mating with humans.