There has never really been a Satan in Marvel, as the closest thing to Him would be Mephisto, who was not actually Satan, but a demonic being mimicking him!..
he seemed to have been shown in Ghost Rider, as when "Jesus" appeared to help Johnny Blaze out, but later retconned to being a fake Jesus and not real satan!
This Satan, explained to Hellcat that he wasn't the Satan from the Bible, and added the caveat that he wasn't sure if that Satan actually exists.
He claimed to be tapped in to the collective Human unconscious, and that all other demons like Mephisto were aspects of him.
The problem, of course, is that this is all coming from the mouth of a demon, so who knows how credible any of it is...