Short answers, pulled from the story.
The term Satanism entered English from French satanisme during the Reformation era between 1517 and 1700. Early usage by Catholic and Protestant groups labeled rival sects as deviants rather than describing actual devil worship.
The earliest recorded accusation within Western Christianity occurred in Toulouse on the 1st of October 1022 when two clerics were tried for venerating a demon. Estimates suggest that between 40,000 and 60,000 people were executed for witchcraft across Europe and North American colonies between 1560 and 1630.
John Milton published his epic poem Paradise Lost in 1667 featuring Satan as the protagonist rather than a mere villain. These writers saw Satan as a metaphor to criticize church power and champion reason and liberty without forming organizations or worshipping Satan.
Religious Satanism began in 1966 with the founding of the Church of Satan by Anton Szandor LaVey in San Francisco, California. His 1969 Satanic Bible sold nearly a million copies despite having very little connection to actual Satan or its worship.
Michael Aquino left the Church of Satan on the 21st of June 1975 to found the Temple of Set where members remain divided on whether Set is real or symbolic. The Temple of Set focuses on enlightened individualism through personal education and initiation while rejecting LaVey's materialist philosophy.
The Satanic Temple based in Salem, Massachusetts became active since 2012 and claims 700,000 members worldwide as of late 2023. Unlike older organizations its congregants do not believe in a supernatural Satan but use it as a metaphor for pragmatic skepticism and personal autonomy.