Johann WeyerJohann Weyer, aka Wierus, Wier (1515—1588) was a German physician, occultist and demonologist, disciple and follower of Heinrich Cornelius Agrippa. He wrote the books De Praestigiis Daemonum (1563) and twenty years later Pseudomonarchia Daemonum (1583) as an appendix to the first.
Weyer criticised the Malleus Maleficarum and the witch hunting by the Christian authorities; he was said to have been the first person that used the term "mentally ill" to designate those women accused of practising witchcraft. In a time of great number of witch trials and executions, he sought to derogate the law concerning witchcraft prosecution.
Some scholars have said that Weyer intended to mock the concept of the hellish hierarchy that previous grimoires had established by writing those two books and entitling his catalogue of demons Pseudomonarchia Daemonum (The Pseudo-monarchy of the Demons).
Nevertheless, meanwhile in De Prestigiis Daemonum (The Illusions of the Demons) he defended the idea that the Devil's power was not so strong as it was said by the Christian church, he defended also the idea that demons had power and could appear before people who called upon them, creating illusions; but he commonly referred to magicians and not to witches when speaking about people who could create illusions, saying they were heretics, using the Devil's power to do it, and when speaking on witches, he used the term mentally ill.
More, Weyer did not only write the catalogue of demons Pseudomonarchia Daemonum, but also gave their description and the conjurations to invoke them in the appropriate hour and in the name of God and the Trinity, not to create illusions but to oblige them to do the conjurer's will, given advice on how to avoid certain perils and tricks if the demon was reluctant to do what he was commanded or a liar; this, together with the fact that he wanted to abolish the prosecution of witches, and that when speaking on those who invoke demons, which he called spirits, he carefully used the word exorcist, suggests the idea that the title Pseudomarchia Daemonum was an attempt to disguise the reality that he could have been not only an investigator on the subject but also a practitioner.
Weyer never denied the existence of the Devil and a huge number of other demons, of high and low hierarchy.
Having been a follower of a renowned occultist like Agrippa, having criticised the Malleus Maleficarum and the witch prosecution, having written two books on demonology, and having been credited as a pioneer in Psychiatry just for using the term mentally ill, Weyer is considered a contradictory character by many authors, but they could never make clear the reason for his alleged contradictions. Perhaps the answer to his contradictions is on the same Malleus Maleficarum: To invoke a demon and oblige him to serve a person in the name of God is not a sin, the sin and heresy consist in asking him.
However it is, he had to read previous grimoires and compilations to write his two works, and books on magic were not at hand to every people. His work was an inspiration for other occultists and demonologists, including an anonymous author who wrote the Lemegeton (The Lesser Key of Solomon). There were many editions of his books (written in Latin), especially Pseudomonarchia Daemonum, and several translations into English, the first by Reginald Scot.