Book of Job
Heads up, everyone: this is not your grandfather's Satan. No red skin, no horns, no pointy teeth and tail, and no devilish grin. This Satan isn't even a tempter yet. In Hebrew, Satan actually means "The Accuser" or "The Prosecutor," and he is referred to as "the" Satan, not just "Satan." It's more of a title than anything else—like "Your Honor" or "the Monsieur."
Satan only pops up in Chapters 1 and 2—when things get poetic, he's out of there for good. We don't have much to go on, but let's take a look.
What We Know About Satan
(1) He spends a good amount of time down on earth. When he presents himself to God and his divine court and God asks him how his life is going, Satan always replies that he's been hanging out on earth. Angels get to do that, apparently.
(2) He isn't a pushover. Satan challenges God not once, but twice. Why does this matter? Well, it kind of makes us wonder if we, too, should be questioning God.
(3) He's pretty powerful. Remember, God doesn't inflict anything nasty on Job with his own divine power. Instead, he allows Satan to use his own power. Having Satan do the dirty work is a very Greek-mythology thing to do—you know, let a demigod do the dirty work, then assert your dominance anyway. But it also makes us think of Satan as the bad guy. He certainly isn't raining down sunshine, rainbows, and love.
Satan doesn't stick around very long. Why? Because, ultimately, this fight is between Job and God. Satan's a catalyst, sure, but the moral of the story lies in man's relationship with God.