Satan is a title. Before the King James Version, the title of Satan was used like a black hat in an old western movie. It’s not any one person or entity, it is whomever acts as the opponent for the specific story.

The KJV wanted to make the Bible more approachable for the average person, because the Church of England had a very “it’s only for the rich and powerful” vibe that it was trying to shake. One of the ways it did this was by simplifying some concepts like Satan, condensing the multiple Satans into a single recurring entity.

That’s also why the KJV leans so heavily into the thee’s and thou’s. That was informal language at the time, mostly used by the peasant class. And if you’re trying to make a book more approachable to the peasants, you write it in peasant-speak. Ironically, we tend to think of “thee” and “thou” as sounding extremely haughty, but it’s because the peasants always emulated the rich. The rich used “you” and “yours” instead, so that’s what the peasants eventually gravitated towards to try and sound proper. And now to modern speakers, “thee” and “thou” sound like they’re from an era of kings and queens, so we tend to associate them with royalty instead of the peasants who actually spoke it.

You’re thinking of Lucifer, who is often God’s henchman before he rebels. His whole schtick was that God would tell Lucifer to go tempt some mortals, to see if they pass His purity test. And Lucifer, being God’s most perfect creation, was immediately disarming and charming. Nobody would be tempted by a dude who obviously looks like a devil. God basically sent Lucifer (the world’s most solid California 10 with a disarming personality) down to earth, to tempt the dirty mortals (who pulled teeth to try and cure the common cold, and had probably never seen anything above an unwashed Iowa 1.5).