Judaism developed a very rich demonology, which was often fed by the various cultures which surrounded the Jewish communities throughout the world. Many early accounts of demons bear a striking resemblance to Egyptian and Persian ideas, while creatures borrowed from French and German folklore were recognized or adopted in the Middle Ages. While many of these supernatural creatures were evil or at least malevolent, what I find particularly fascinating is the very un-Christian notion that not all demons were anti-God, nor were all sent by Satan. Would you believe me if I told you it was believed that some "Jewish demons" worked for God, punishing sinners? What if I told you it was believed that others studied the Torah?
It might make you uncomfortable. Taken out of context, it could lead someone to wonder if Jews are devil-worshippers or something equally ridiculous. Well, if you're wondering, they're not. They never were. They were as afraid of demons as Christians, for much the same reasons. They used demons in stories to represent temptation to sin, and the force of evil working against the righteous. They performed exorcisms, too. But they also had interesting stories, and in some of them, the demons were Jewish.
This did not, however, imply that demons liked humans, Jew or otherwise. Nor did it imply we should ask them out to lunch.
The Zohar, one of the most important books on the Kabbalah ever written, distinguished between three types of demons: Those which are similar to angels, those resembling humans, and those which pay no respect to God, and are like animals.
Demons are said to resemble angels in that they fly and have no permanent physical form. They are said to resemble humans in that they eat, reproduce, and (eventually) die.
Based on Jewish folklore and superstition, we can assign most demons to one of three three categories:
1. "Jewish" Demons. At the end of the sixth day of Creation, God went about making demons, creatures which were to be angel-like. He had made their souls and given them their intelligence and power, but ran out of time before the Sabbath, and so the demons had no bodies, nor were they ever completed. These demons were His creations, God-fearing, and subject to Him. However, because of their unfinished state, they became resentful and jealous of humankind. These demons are sometimes referred to as "sublunar" (that is, earthly) demons. They were considered to be Jewish, even so far as getting married in Jewish fashion and circumcising their children!
As a general rule, these demons didn't actively seek to harm human beings unless they had a good reason; for example, if they had been bound against their will or trapped, their home had been trespassed, they had been provoked, etc."Demons will torment only people who annoy them," Rabbi Judah he-Hasid wrote in Sefer Hasidim (The Book of the Pious). He goes on to elaborate, citing a number of activities which annoy demons. One is performing witchcraft (which is NOT practical Kabblah), an activity which was widely believed to involve the summoning and binding of demons.
Ashmedai (also known as Asmodeus) is often called the king of the Jewish demons, many of whom study Torah, and will not harm a human Torah scholar! Ashmedai himself is said to ascend to Heaven to study. He also seems to have a sense of humor with a mean streak; there are a number of stories concerning him getting the better of King Solomon when the King become cocky with him.
Ashmedai's demons are subject to God, and are sometimes found in His service to punish the impious or evil. For example, those who commit sins or break purity laws may be subject to attack. There is a demon who punishes those who mistreat holy books. Not an angel, but a demon! In another example, Rabbi Judah writes one must not step on crumbs, for "The demon of poverty resents it when a person steps on breadcrumbs. He says, 'After this fellow filled his belly with bread, he steps on the leftovers. [He is so ruthless] he would destroy the whole world if he could.' Therefore, the demon torments him."
Some of these original demons, like Samael and his host, are purely evil. These are more akin to the "fallen angels" of Christianity.
2. Lilith and Her Offspring. According to legend, before Eve, God made Lilith, much as He made Adam. Although Adam considered himself the superior, Lilith didn't agree, claiming she was her own person. They quarreled constantly (particularly about sex, some sources state), until finally Lilith became enraged and fled the Garden of Eden. She settled in a cave, where her relations with demons produced the first of her children. Unlike the "original" demons, Lilith and her hybrid children are typically malicious and actively seek to harm humans in one way or another.
Lilith is at the center of many stories and superstitions. You can read more about Lilith in the essay dedicated to her.
3. The Minions of Sitra Akhra. Sitra Akhra could be translated "the other side". Some philosophers believed that all things were created by and subject to God (including demons), but others wondered if the things which were so unspeakably evil had their origins in another realm outside of God's command, or at least if there was a place forsaken by God, or where the inhabitants had no respect for God at all. This produced the idea of Sitra Akhra, which I suppose is the closest I've seen to a classical Hell in the Christian sense, where the inhabitants are purely evil and have completely forsaken God, existing only to satisfy their perverted whims. The demon Samael (who is often equated with Satan) is sometimes said to live here. Anything from Sitra Akhra would be completely evil, malevolent, and very dangerous.