I Am Satan! Destroyer of Evil!
Is Satan a bad guy? Well, sure. But why? If he punishes evil, why is he the bad guy? Certainly that should make him the good guy, right?
Well, it isn't a matter of him punishing evil. In fact, he doesn't punish evil at all. Satan is awaiting his punishment and is trying to drag down as many people with him as possible. He doesn't sit on a fiery throne in Hell dealing out punishment: no, no, no. It is a common misconception (and a frequent misrepresentation) for that to be the case. But it is not the case.
Satan woke up one day and challenged God's authority. He was outcast for trying and wanting to usurp God's throne, and he was doomed to be punished eternally in Hell. He now temps everyone and tries to keep people away from God, that way he can drag as many people down to Hell with him as possible. If he can't have it, why should you be able to? He tries to get Christians to stop following so closely: to become more complacent and content with where they are at in their faith, that way they never reach out to others. Believers and unbelievers get tempted all the same. If he tempts unbelievers, he can keep them away from God. If he tempts believers, the unbeliever will never be witnessed to. The Word will never reach his ears.
Some day soon, Satan will be in Hell with the unbelievers being punished, not dealing out punishment.
Now, if you want to talk about a Satan that is misunderstood, let's talk about Hades.
Hades was a chill dude. He was loyal. He stayed true to his wife (mostly). He wasn't nearly as screwed up as the other Greek gods. He was nice. He was a good father... and yet he has such a bad rap. Not to mention, he has a cute doggo named Cerberus. Now that's how you know he is a good man: he has a good pup.