Short answers, pulled from the story.
The Church of Satan was founded in 1966 by Anton Szandor LaVey in San Francisco, California. It is considered the oldest continuous Satanic organization and has had the most influence on subsequent Satanic groups.
The Satanic Bible, published by Anton LaVey in 1969, is the most influential statement of Satanic theology and sold nearly a million copies. It draws on the Romantic literary concept of Satan as a rebel anti-hero rather than on supernatural belief, combining humanism, hedonism, and Social Darwinism.
Between 40,000 and 60,000 people were executed during the European witch trials of the fifteenth to eighteenth centuries, with executions peaking between 1560 and 1630. Historians broadly agree that the majority of those persecuted had no involvement in Devil worship.
FBI agent Ken Lanning investigated 300 allegations of Satanic ritual abuse and found no evidence of Satanism or ritualistic activity in any of them. In the UK, anthropologist Jean La Fontaine similarly found no evidence of Satanist group involvement or murders in the cases she examined for the Department of Health.
The Satanic Temple is a nontheistic Satanic organization based in Salem, Massachusetts, active since 2012, which claimed 700,000 members worldwide as of late 2023. It uses the literary figure of Satan as a metaphor for skepticism and personal autonomy, and focuses on political activism around church-state separation and civil liberties.
Theistic Satanists venerate Satan as an actual supernatural deity or force, sometimes including belief in magic and ritual devotion. Nontheistic Satanists, who appear to form the majority of contemporary Satanists according to surveys, regard Satan as a symbol of certain human traits or a metaphor without supernatural reality.