Modern rationalist satanismo starts with the jesuit educated French philosophe and usurer to the crowned heads of Europe, lyricist, playwrite and incestuous pedovore Francois-Marie Arouet, aka "Voltaire."

"Voltaire was a versatile and prolific writer, producing works in almost every literary form, including plays, poems, novels, essays, and historical and scientific works. He wrote more than 20,000 letters and more than 2,000 books and pamphlets. He was an outspoken advocate of civil liberties, despite the risk this placed him in under the strict censorship laws of the time. As a satirical polemicist, he frequently made use of his works to criticize intolerance, religious dogma, and the French institutions of his day."

Francis pretense of impartiality (maintained in writings for publication) is dropped in his personal correspondence.

" In a letter to Frederick II, King of Prussia, dated 5 January 1767, he wrote about Christianity:

La nôtre [religion] est sans contredit la plus ridicule, la plus absurde, et la plus sanguinaire qui ait jamais infecté le monde.
"Ours [i.e., the Christian religion] is assuredly the most ridiculous, the most absurd and the most bloody religion which has ever infected this world. Your Majesty will do the human race an eternal service by extirpating this infamous superstition, I do not say among the rabble, who are not worthy of being enlightened and who are apt for every yoke; I say among honest people, among men who think, among those who wish to think. ... My one regret in dying is that I cannot aid you in this noble enterprise, the finest and most respectable which the human mind can point out."

https://en.wikipedia.org/wiki/Voltaire#Christianity

Anon Wolfgang Mozart remarked at Marie's death:

"...deeply Christian Wolfgang Amadeus Mozart wrote to his father the year of Voltaire's death, saying, "The arch-scoundrel Voltaire has finally kicked the bucket ..."