Two types of people were accused of worshipping Satan during the Middle Ages and Renaissance: witches and Western esoterics. The late 15th-century treatise on witchcraft "Malleus Maleficarum," aka "Witches' Hammer," followed the contemporary culture's lead of labeling everything in opposition to orthodox Christianity as Satan worship. It contained sections condemning witches for disbelief in demonology and having sexual relationships with devils. And groups like the Cathars were considered heretics and persecuted by the Church for revering Satanic figures.
Despite the accusations, there's no hard evidence of organized groups worshipping Satan as an evil deity in the Middle Ages or Renaissance. And the existence of some supposedly devil-worshipping groups, like the Luciferians, is debated and often discredited as a smear tactic. Were there really organizations, covens or cults that regularly worshipped Satan at the time? The short answer is almost certainly not.
For the long answer, let's start with witches. During the 16th and 17th centuries, a widespread witch panic in Europe hit its peak. An estimated 60,000 people in Europe and the American Colonies were sentenced to death for the crime of witchcraft, almost all of them women [source: Bailey]. That witchcraft hysteria was famously exported to the U.S. via Salem, Massachusetts, in 1692. The overwhelming majority of these cases were the result of petty grudges, childish accusations or social punishments. Some of the "witches" involved were practitioners of older pagan traditions or folk magic, or were simply insufficiently pious in the eyes of the local community [source: Goodheart]. In her 1978 journal article on witch hysteria in medieval Europe, author Mary Ann Campbell explains, "the negative image of the witch as evil, as deviant, was created by the Christian Church with the help of the secular ruling class. The 'One True Church' had to eliminate the competition."
Then there are esoteric orders, or groups that subscribed to nonmainstream Christian ideas or adopted occult practices from other religions. These included groups that practiced gnosticism, kabbalah, Christian theosophy and Rosicrucianism. What they all had in common is the idea that there are hidden (occult) truths to be found in the world or in sacred texts, and members could learn rituals that unlocked secret powers.
Esoteric orders were not overtly Satanic. However, the mainstream church depicted them as evil and Satanic to undermine them and reduce their appeal, much as they'd done with displaced religions in earlier eras. For example, in the 14th century power struggle between church authorities and the Christian military order Knights Templar, the leaders of the Knights were arrested and accused of spitting on the cross and worshipping an idol called Baphomet.
The inherent secrecy of these groups left them vulnerable to accusations of blasphemy and Satan worship. The members of these orders may have been branded as wicked heretics and blaspheming devil worshippers, but it is unlikely that there were any long-term organized groups of Satanists actively worshipping Satan as an evil entity in any historical era. Even today, secret societies and esoteric orders like the Illuminati and Freemasons are at the heart of many sinister conspiracy theories. There's a plot twist, though: Modern Satanist groups have adopted many supposedly Satanic symbols, like the inverted pentagram and image of the deity Baphomet, used by esoteric orders.
That said, it's time to meet Anton LaVey, the father of modern Satanism.