The Church of Satan was founded in San Francisco in 1966 by Anton LaVey, a former organist and carnival worker with a talent for publicity. Its text, The Satanic Bible, appeared in 1969 and has remained in print ever since. Much of the book is LaVey's own, but its opening Book of Satan is taken with little acknowledgement from Might Is Right, an 1896 tract by the pseudonymous Ragnar Redbeard, a work of aggressive social Darwinism whose politics sit uneasily with later Satanist self-description. The Church remains deliberately small and non-activist. It does not lobby, does not litigate, and describes itself as a religion of the individual; leadership passed after LaVey's death in 1997 to Peter Gilmore, and membership figures are not published.
The Satanic Temple grew out of a 2012 collaboration between Lucien Greaves and Malcolm Jarry and was publicly active from 2013. Its method is legal rather than ritual. Where a government body grants a privilege to one religion, it requests the identical privilege and litigates when refused. It commissioned a bronze Baphomet monument and sought its placement beside Ten Commandments monuments at the Oklahoma and Arkansas state capitols; the Oklahoma monument was removed after the state supreme court ruled against it, and the Arkansas case ran for years. It has run After School Satan clubs where evangelical clubs are permitted in public elementary schools, and has brought religious-liberty claims concerning abortion access on the basis of its tenet of bodily inviolability. The United States tax authorities recognised it as a church in 2019, a designation it sought precisely because it forecloses the argument that it is not a real religion.
The two are not allies. The Church of Satan regards the Temple as a political pressure group misusing the name, and the Temple regards the Church as inert. They also differ on whether Satanism should be public and adversarial toward the state or private and indifferent to it. Both, again, are atheistic; the disagreement is about what an atheistic religion built on that symbol ought to do.