Simplify the following text for a Grade 9 native English-speaking person.
Original: The Church of Satan was established at the Black House in San Francisco , California , on Walpurgisnacht , April 30 , 1966 , by Anton Szandor LaVey , who was the Church 's High Priest until his death in 1997 .
Simplified: The Church of Satan started in San Francisco , California , on Walpurgis night April 30 1966 , by Anton Szandor LaVey , who was the Church 's high priest until he died in 1997 .