When I was a teenager, I went to church, and almost every ‘Christian’ there was a complete asshole. What makes it worse is that they try to justify it. This honestly made me think that if God and Satan were real, I’d want to know Lucifer’s story. Maybe he’s not actually ‘evil.’
Lucifer existed before but didn’t become entangled with Satan until after christianity had roots. So it is a post biblical merge, but pre-biblical. The concept is older, the merge changed the focus of the concept.(69 is just number, until it becomes a joke as well.)
Satan and more properly the ‘Devil’ as is the main concept in modernity. This is due to the romans using this translation preferably from the Greeks. The devil then got most of their iconography from Pan and some roman art traditions. This is far more important than people realize. Anyways, all this was forming in the roman zeitgeist while Christianity was not canonical to the empire yet.