Satanism is a word which has been used over the years to describe a number of different belief systems in a number of contexts. People claiming to be Satanists, or outsiders claiming to describe Satanism, ascribe a wide variety of beliefs to Satanism. These range from the literal worship of a malevolent spiritual being (Theistic Satanism); to a kind of subversive ritual performance stressing the mockery of Christian symbols (most notably the “Black Mass”); to the claimed rediscovery of an ancient but misunderstood religion (e.g. Setianism, which conflates Satan with the Egyptian god Set); to the exaltation of hedonistic recreation, and the celebration of selfishness and pleasure.
The most prominent and widely known Satanist in recent years is, and was Anton Szandor LaVey, who founded the “Church of Satan” in 1966. LaVey wrote The Satanic Bible (1969) and other works which remain highly influential (though controversial) among avowed Satanists. LaVey rejects the Black Mass, cruelty to animals, or a literal belief in (or worship of) Satan, instead considering Satan as the human instinct within ourselves, which is what LaVeyan Satanism celebrates; the human instinct. Instead he supports a view of human beings as animals and rejects many social structures that he believes inhibit human instincts.
Equally celebrated within certain, though not all, Satanic circles (and not technically a Satanist) would be ritual magician Aleister Crowley, who referred to himself as "The Great Beast 666." Aleister Crowley, though not a worshiper of any deity known as Satan, his severe disdain for Christianity and his occult activities have been confused and conflated into his fame as a "Satanist". As an aside, culture has made the word "Satanism" what it is today. Thus the word "Satanism" would have never have been birthed into existence if it wasn't for a Christianity that was afraid of a person or group of people who would use the mass, religious garments, sacred scripture, or symbols in order to worship in a way antithetical to the Christian religion and worldview. "Satanism" as a word and as an "ism" is not often associated with individual or groups who do not believe in Satan, but from the beginning of the use of the term "Satanism", that is exactly how it was applied. "Satanism" is a myth, and, just like the word "witch" will always call to mind the image of a popular Halloween costume involving a hat, long nose, and broom. "Satanism" will always have the image and, more importantly, will always have the meaning of the mythic image of people doing naughty things that transgress Christianity. If someone in modern times wanted to be "Satanic", in that light one must believe in the Christianity, its power, and break its taboos to transgress them to fulfill the image of the dreaded, abhorred, evil Satanist.
Much "Satanic" lore does not originate from actual Satanists, but from Christians. Best-known would be the medieval folklore and theology surrounding demons and witches. A more recent example is the so-called “Satanic ritual abuse” scare of the 1980s, beginning with the memoir Michelle Remembers--which depicts Satanism as a vast conspiracy of elites with a predilection for child-molesting and human sacrifice. This genre regularly describes Satan as actually appearing in person in order to receive worship. It must be noted that this is not adhering to the teachings of the Church of Satan, which is strictly against child abuse, rape or any other fully harmful sadistic act, especially to children. Consensual S&M between adults is advocated on the grounds that it is a form of self-gratification.
Another prominent source of "Satanic" imagery is black metal music, which has given Satanism the "Hail Satan!" hand-sign. A few rock stars such as Marilyn Manson (alternative rock, industrial artist) appear to actually be bona fide Satanists; many others merely adopt a pseudo-Satanic persona for the sake of romanticism.
Vandalism, cruelty to animals, or grave desecration are advanced by some as examples of satanic crimes. While some high-profile cases of murder or serial murder have been found to have Satanic themes (e.g. the Manson Family), these appear to be primarily the work of disturbed individuals, or of several acting together, rather than of organized religious groups.
Many claims of Satanic child-molesting or murder rings have proven to be unsubstantiated. There was little evidence to support the allegations. Few people were convicted though there are now organized efforts to have the charges dropped.