The first thing you need to know is that a true Satanist will tell you that any group that puts Satanic imagery on their album covers or in the music is bogus. Every single one.
The other thing you need to know is that a true Satanist will also tell you that all music is Satanic, every single note.
Consequently, an article on Satanic rock is a tricky proposition insofar as none of it is real; explicitly Satanic rock like Venom is really no more Satanic than The Carpenters. And the Carpenters are just as Satanic as Venom.
However, there is a history to the appearance of Satanic imagery and references in rock music. So consider this an attempt to organize that history a little.