Actually, he was a good guy (played by Billy D. Williams) in the first Tim Burtan Batman movie and the villain in the third one of that series (played by Tommy Lee Jones).
The Spiderman movies - the son of the Green Goblin dude (Harry Osborne?).
Mark Harmon played a doctor on St. Elsewhere who became a rapist after several seasons.
Dr. Peter White on St. Elswhere might fit your guidelines, depending on how you use the term “good guy.” He was portrayed as kind of a fuck-up, but generally a sympathetic character and the best friend of David Morse’s character (who was arguably the main protaganist of the entire series).
At the end of the second season, Dr. White was revealed to be the masked rapist who’d been attacking women at the hospital, and was subsequently shot to death by a nurse.
Edit:
Peter White was played by Terence Knox. Harmon’s Dr. Robert Caldwell was not a rapist, but he was a horndog who caught AIDS and eventually died.
I believe Harvey Dent should count. According to The Dark Knight, he was good waaaaaay before the movie began, and we have no reason to doubt that. In the end, it’s the events in the movie itself that turn him.
Right as rain, you are. Sorry about that. It’s been a long time, and I never watched in reruns after being disappointed by the finale. I shoulda looked it up.
Detective Tony Profaci on Law & Order was a good guy for several seasons, but in the made for TV movie Exiled, which focused on Mike Logan on Staten Island, it was revealed that he was dirty.
Jonathan from Buffy: The Vampire Slayer should probably count. Granted he wasn’t an effective or particularly evil bad guy, but he meets all the requirements of the OP.
In fairness to Londo, he never really reveled in genocide. He wanted to restore the Centauri Republic as a superpower, and got himself so deeply beholden to the Shadows and unscrupulous elements of the Centauri court that he couldn’t stop the genocide. And he certainly does try to justify the thing later on, in his capacity as the Republic’s Ambassador.
But look at the man’s face when he’s aboard the Centauri warship, watching the bombardment of Narn. He’s horrified, and appalled, and he never, ever wanted that.
The tragic thing about Londo’s character is that he’s a decent man whose concepts of good and patriotism drive him to do unspeakably terrible things. And he pays for them - far more than anyone should have to pay, I think.
The problem is that Londo was born long after the height of Centauri power- he grew up with stories of the glory of Empire, and believed them, but never understood just how bloody a thing Empire always is. So he wished for it, and got it.
How about Ro Laren? Pulled a phaser on Riker and betrayed Starfleet’s mission so she could go join the Maquis. I’m not sure how “bad” that makes her, but she surely would’ve been court martialed.
Getting back to the OP - Boyd Langton from Dollhouse would certainly qualify. He spent the first season as Echo’s stalwart handler and protector, and is revealed at the end of the second season to be the evil head of the Rossum Corporation.
The really messed-up bit is that Echo had, of course, been conditioned to trust Langton implicitly. The betrayal in her voice when she says to Langton, “I trusted you,” was one of Eliza Dushku’s better acting moments.
Evil Willow fits all of the OP’s requirements, although she was only “bad” for a few episodes. But that was a clear-cut case of a good guy choosing to be evil, rather than being influenced by some external manipulator.
I’ve seen strong arguments posted elsewhere on the Dope that, although Willow was only running around killing people for a few episodes, she was pretty much always a terrible person - mad, bad, and dangerous to know. She brainwashed her girlfriend and tried to kill Dawn before turning “evil”, for example.
She was really unstable in that season (though she did not try to kill Dawn! She put her in harm’s way, but didn’t actually try to kill her) but there’s no way she was mad, bad and dangerous to know in earlier seasons.
So she counts, I reckon, as does Jonathon.
Well there is Captain Sisko from Deep Space Nine but he is the only one who knows he is ‘bad’. Another character Garrick knows but doesn’t think what they did was wrong.
But Sisko knows what he did was wrong and completely against his code but he did it anyway ‘for the greater good’.
True. That’s the moment he changes back. But from the point where Morden asks him “What do you want?” until that moment, Londo gets darker and darker and revels in the fact that Narn will be destroyed. It is only when he actually sees it happening that he realizes he went too far.
Your use of that term reminded me of President Allison Taylor on 24. In season 7 she was a bastion of integrity, even having her own daughter arrested rather than pull strings on her behalf.
By the end of season 8, having been corrupted by ex-President Logan, she’s stifling the press, covering up murders, and tacitly approving Jack Bauer’s assassination – all justified in her mind ‘for the greater good’. Even though she kind of comes back around in the end, she ends the season about to resign in disgrace.
Except for being a **main **good guy.
Willow, however, certainly counts.
David Mills in Se7en.
Doesn’t this happen all the time in Pro Wrestling?